Abstract: A cushion for a chair including a seat member and a back-supporting member, wherein the seat member includes two ischium-facing portions, a surface of each ischium-facing portion abutting an ischium of the user and having a specific three-dimensional curved surface; and the back-supporting member includes an ilium upper border-facing portion and a lower ribs-facing portion, a surface of the ilium upper border-facing portion abutting an ilium of the user and being entirely concavely curved in a transverse cross section along a left-right direction, a surface of the lower ribs-facing portion abutting the lower ribs of the user and being entirely concavely curved in the transverse cross section along the left-right direction, and a portion of the back-supporting member upper than the lower ribs-facing portion having a specific three-dimensional curved surface.

Abstract: A cushion for a chair including a seat member and a back-supporting member, wherein the seat member includes two ischium-facing portions, a surface of each ischium-facing portion abutting an ischium of the user and having a specific three-dimensional curved surface; and the back-supporting member includes an ilium upper border-facing portion and a lower ribs-facing portion, a surface of the ilium upper border-facing portion abutting an ilium of the user and being entirely concavely curved in a transverse cross section along a left-right direction, a surface of the lower ribs-facing portion abutting the lower ribs of the user and being entirely concavely curved in the transverse cross section along the left-right direction, and a portion of the back-supporting member upper than the lower ribs-facing portion having a specific three-dimensional curved surface.

Abstract: A seat device has an upper body support member having an upper body support surface that supports an upper back of a person. The support surface has aid ridges for shoulder blades. The aid ridges are located to be fit to a range of fifth to seventh ribs of the ribs in a vertical direction of the seat member, and are substantially horizontal in a width direction of the seat device. The support surface is located such that a length from a center line of the support surface in a width direction thereof to a center-line-side end of each of the aid ridges is equal to or larger than a length from a backbone center line to a backbone end of the person and equal to or smaller than a length from the backbone center line to a shoulder blade of the person.

Abstract: A device for retaining a person's seated position is provided as seats for vehicles, for example. The device has a seat member and an upper body support member. The seat member has a seat surface on which a person is seated. The seat surface has a pair of reference ridges each of which is fit to a recess between a biceps femoris muscle and a semimembranosus muscle of each of thighs of the person. The upper body support member has an upper body support surface that supports an upper body back of the person. Various types of ridges are provided on the upper body support surfaces for stabilizing the upper body of the person seated on the seat.

Abstract: A seat device capable of retaining a person's seated position is provided as seats for vehicles, for example. The seat device has an upper body support member having an upper body support surface that supports an upper body back of a person seated. The upper body support surface has slant ridges for ribs. The slant ridges can touch the ribs of the person from beneath and are slanted according to the ribs, the ribs descending with person's exhalation.

Abstract: A device for retaining a person' seated position is provided as seats for vehicles, for example. The device has a seat member and an upper body support member. The seat member a seat surface on which a person is seated. The upper body support member has an upper body support surface that supports an upper body back of the person. The upper body support surface has a pair of support projections for ilia, which are fit to a pair of ilium projections of the person, the ilium projections being projected rearward when the person is seated on the seat surface of the seat member. The seat surface has a pair of accommodating recesses for ischiums, which accommodates therein a pair of ischium projected portions of the person, the ischium projected portions being projected downward.