A gear engagement mechanism of a life device includes a lifting member interlocking with a lifting tray to linearly move in a vertical direction, and a gear train having a pinion engaged with the rack to transmit a rotary motion to the rack and transmitting the rotation torque of a lift motor M to the pinion. When the lifting member has over-run an upper limit stop position and a lower limit stop position, engagement of the pinion and the rack is released.