To provide a seating/standing assist device and chair having a seating/standing assist function at a low cost, the seating/standing assist device allowing a user to safely perform seating/standing and, when seating, to be deeply seated on a seat face of a chair in a simple structure without any complicated structure.SOLUTION: A seating/standing assist device 1 includes: side frames 100 installed longitudinally at both sides of a seat face of a chair 2； a seat face frame 200 formed into a substantially U-shape having the width substantially coinciding with the horizontal width of the seat face of the chair, in which a sitting seat 210 is installed on a rear face thereof； energizing means 230 for energizing in a direction to flip up a rear end side of the seat face frame； and a seat face locking mechanism 500 for locking rotation of the seat face frame after the seating. A rotation center of the seat face frame is supported by the side frames so as to be located forward a front end of the seat face of the chair, such that the seating/standing assist device can support the buttocks of a user to a high position thereof, while preventing inclination of the seat face from getting a steep angle, when seating/standing. The seating/standing assist device further includes handrails 300 for stabilizing a posture in the seating/standing action and during the seating.SELECTED DRAWING: Figure 1【課題】複雑な機構を要することなく簡単な構造で着座・起立を安全に行うことができ、着座に際して椅子の座面に深く腰掛けることができる着座起立補助装置および着座起立補助機能を有する椅子を低価格で提供する。【解決手段】着座起立補助装置１は、椅子２の座面の両サイドにおいて前後方向に設置されるサイドフレーム１００と、椅子の座面の左右幅と略一致する幅を有する略Ｕ字形に形成され、裏面に着座面１２０が装着される座面フレーム２００と、座面フレームの後端側を跳ね上げる方向に付勢する付勢手段２３０と、着座後に座面フレームの回転をロックする座面ロック機構５００とを備え、着座・起立に際して座面の傾斜が急角度とならずに使用者の臀部を高い位置までサポートできるように、座面フレームの回転中心が椅子の座面の前端に対して前方に有するようにサイドフレームに支持される。また、着座・起立動作および着座中の姿勢の安定化を図るためのハンドレール３００を備える。【選択図】図１
