As described in patent document 1 for example, a dual-pinion electric power steering device having two pinion shafts is known.  In this dual-pinion electric power steering device, one of the two pinion shafts is connected to a steering shaft and the other one of the dual pinion shafts is connected to a motor that increases (assists) a steering force. 
A rack shaft moves left or right in a vehicle width direction by a mesh operation with the two pinion shafts.  A reaction force acts on the rack shaft by the two pinion shafts such that the rack shaft and the pinion shafts separate from each other.  For this reason, for each of the two pinion shafts, it is necessary to press a back surface of the rack shaft by a rack guide.