To provide a load body driving device for opening and closing a flow passage by reciprocating a load body like a gate, of which the driving device has a compact, safe and trusty structure.

The load body driving device comprises a motor 1 for reciprocating the load body 20 mounted on a pin rack 10, and a power transmission device 14 converting and transmitting a rotating motion to a reciprocating motion of the load body 20. The power transmission device 14 comprises a non-excitation operation maintaining brake 3 provided on a transmission shaft 42 rotated by the motor 1, a primary decelerator 5 which is connected to a manual handle 7 by the intermediary of a worm gear 35 and is connected to the transmission shaft 42, a pinion shaft 11 mounted on a secondary decelerator 6 connected to the primary decelerator 5, and the pin rack 10 provided with rack pins 16 engaged with a pinion 9 of the pinion shaft 11.