PROBLEM TO BE SOLVED: To provide an assist device of a movable body capable of a smooth move-back operation from an end position.SOLUTION: An assist device 1 of a movable body related to one embodiment of the invention includes: a pair of contact receiving bodies 10 and 10 provided on one side of a support F and a movable body M slidably moved relative to the support F; a base body 21 provided on the other side of the support F and the movable body M; a pair of abutting bodies 22 provided on the base boy 21, capable of being engaged and disengaged to/from the pair of contact receiving bodies 10 respectively and movable in the slide direction to the base body 21 in the state of being engaged with the contact receiving bodies 10; an energizing mechanism 23 for energizing the abutting body 22 on one side in the slide direction of the pair of abutting bodies 22 toward the other side in the slide direction to the base body 21; and a brake mechanism 24 for imparting resistance force to the movement of the pair of abutting bodies 22.