A chair is provided in which a seat-receiving member is provided with outward flanges for regulating upward/downward displacement to support left and right lateral edges of a seat plate. Engaging grooves supported by the outward flanges are provided at the respective left and right lateral edges of the seat plate. Warpage allowable parts in which warpage deformation of the lateral edges is allowed without the upward displacement being regulated by the seat receiving member are provided in regions of the left and right lateral edges of the seat plate, in which the regions are located at a rear side from engagement parts between the engaging grooves and the outward flanges. With this constitution, it is possible to prevent the seat plate from being detached from the seat-receiving member while ensuring that, when an user is seated, the sides of the buttocks of the user are reliably held, and thus improve the seating stability of a seat body.