An instant film unit advancing apparatus of reduced size, which avoids failure of a discharging film unit when a slip arises between a pair of spreading rollers and the film unit. Components to drive and support the pair of rollers and a picking claw for thrusting the film unit to a bite of the pair of rollers are arranged within the width of a film unit pack. Spreading rollers supporting means support a surface of the spreading rollers, and a driving power source unit includes a motor and a reducing gear train whose shafts are parallel to the spreading rollers. A rotating cam shaft moves the picking claw, which is also parallel to the spreading rollers, instead of a large cam plate used in conventional apparatuses. The cam shaft and a featured mechanism keep rotation of the spreading rollers independent from a cam mechanism for moving the picking claw.