To provide a collapsible chair housed in a wall which can be easily used without anxiety even by an aged person and a physically handicapped person, and without disturbing the going in and out of the person in a porch and an external appearance, and a hinge unit used for the collapsible chair.

This wall housing type collapsible chair 1 is provided in a housing space 7 formed by hollowing out a part of a wall surface 5, is housed in the housing space 7 in a folding up state at unused time, constitutes a part of the wall surface 5, is pulled out forward at using time, and is constituted so as to function as the chair. The hinge unit 3 includes a hinge casing 33 installed on the wall surface 5 in a fixed state, an energizing means for imparting a springing-up tendency to a seat frame 17 housed in the hinge casing 33, a movable joint 15 installed on one end of the seat frame 17 in a fixed state, and turnably connected to the hinge casing 33 with a rotary pin 11.