Sheet feeding device and sheet processing apparatus

A sheet feeding device includes an elastic support member, a following movable member disposed so as to contact an uppermost sheet of a stack of sheets stacked on a sheet tray and can follow and move in accordance with the change in the stacking amount of the sheets, a restraining mechanism that restrains the elastic support member in accordance with the stacking amount of the sheets so that the position of the uppermost sheet is held at a substantial constant, and a release mechanism that interlocks with the movement of the following movable member to release the restrained state. The restraining mechanism includes an engagement member that moves together with the elastic support member and a restraining member that restrains the movement of the engagement member. The restraining member moves along a straight locus at least near an engaging portion to engage with and disengage from the engagement member.