Abstract: A sliding door opening and closing device that horizontally opens and closes the sliding door with application of light weight is provided. A load-type door opening and closing device includes: a sliding support rail slidably supporting the door to open and close the door; a door opening rail provided in the door and inclined upward in an opening direction of the door; a sliding member sliding on the door opening rail; a footboard; and a coupling member that couples the sliding member with the footboard. The sliding member is located at an upper end side of the door opening rail when the door is closed, and is depressed against the door opening rail by stepping force acting on the footboard during opening operation, to displace the door in the opening direction.

Abstract: A door opening and closing device for a slide door, which can be horizontally open and close the slide door by application of a light load and which can be constructed and maintained at low costs. The door opening and closing device has a transmission mechanism for converting through a lever (31) the amount of settlement of a tread plate (21) placed on floor surfaces at positions in front and back of the slide door (12), into a predetermined displacement amount. The tread plate (21) is weight-wise balanced such that the transmission mechanism and settlement of the tread plate due to the weight of an adjustment weight (W) causes the tread plate (21) to float through the lever (31). Up-down movement of the long transmission member (32) presses a drive rotation body (42) to an open door rail (41), and a component force of the pressing force allows the slide door (12) to be opened by application of a light load.