A forward movement mechanism of a movable body is provided with a receiving member which is housed movably in a main body housed in a recess provided in one of a movable body and a fixed body reciprocably supporting the movable body and connected with an assist means which moves the movable body forward to a predetermined position; and a contact body which is provided at the other of the movable body and the fixed body and moved within the main body in contact with the receiving member in the process of the forward movement of the movable body. The moving place of the receiving member in the main body comprises a wall part which guides the movement of the receiving member and a wall part deformation prevention means next to the wall part.