Abstract: A mail enclosing and sealing apparatus (50) in which an envelope (1, 200) is pulled out from an envelope guide (54) in an envelope hopper (52) which stacks the envelopes one by one, the envelope being fed to a gripper means (60) displaced on an envelope transferring belt (58) being driven intermittently, and transferred under the movement of the belt (58) while being held by the gripper means (60), with a flap portion being opened at a given position (S2), and is then transferred to a further position (S3), with the envelope (1, 200) being opened by an opening means (62), and an enclosure (66) transferred from an other route (64) being enclosed in the envelope, then the envelope (1, 200) with the enclosure (66) is transferred to a further position (S4), then said envelope (1, 200) being displaced in a direction crossing the flow of the belt (58) and route (64) to be sealed; wherein the position adjustment of the opening means (62) and the adjustment of the side guide widthwise direction control axis (90) for