In a power steering device employing a hydraulic power cylinder, a motor-driven pump, and a driving power source for the motor, a power steering control system is configured to electrically connected to at least the motor and the power source for controlling a driving state of the motor and a power source voltage of the power source. The power steering control system includes a motor control circuit that generates a motor driving signal, whose command signal value is determined based on a steering assist force applied through the power cylinder to steered road wheels, a booster circuit that boosts the power source voltage, a motor angular acceleration detection circuit that detects or estimates a motor angular acceleration, and a booster-circuit control circuit that controls, responsively to the motor angular acceleration, switching between operating and non-operating states of the booster circuit.