A variable gear ratio hydraulic power steering device 1 is provided with a
variable ratio transmission mechanism 7 for varying the rotation
transmission ratio between the rotational angle of a steering handle 31
and the rotational angle of a pinion shaft 33 and a flow volume control
valve 40 for controlling the discharge flow volume of an oil pump 10
which circulates operating fluid. The variable ratio transmission
mechanism 7 has a lock mechanism 75. A valve controlling controller 50
for controlling the flow volume control valve 40 switches main and
secondary flow volume control maps for controlling the flow volume
control valve 40, in dependence on the operational state of the lock
mechanism 75. Thus, a failsafe function for the variable ratio
transmission mechanism 7 is given to the variable gear ratio hydraulic
power steering device 1.