An interlock system includes first and second racks movable in parallel to each other in a longitudinal direction between opening and closing positions in conjunction with opening and closing of the first cover, respectively. A housing is provided to slidably accommodate the first and second racks in the longitudinal direction. A pinion unit is provided and is sandwiched by the first and second racks. The first and second racks have meshing sections respectively meshing with the pinion unit at one side surfaces extending in the longitudinal direction facing each other. The pinion unit slides in the longitudinal direction by a prescribed length in conjunction with movement of at least one of the first and second racks. The interlock switch is turned on and off in accordance with a sliding length of the pinion unit in the longitudinal direction.