To provide a pulse amplitude modulation controller wherein when the speed of a permanent-magnet synchronous motor is controlled using a pulse-width-modulation voltage inverter, the limit of direct-current link voltage that limits operating speed is reduced and optimal control can be implemented over a wide speed range.

The pulse amplitude modulation (PAM) controller is so constructed that: a bidirectional step-up/down converter circuit 30 is connected to the output terminals of an accumulator 40; a PWM voltage inverter circuit 20 is connected to the output of the converter circuit; and a variable-speed permanent-magnet synchronous motor 10 is connected to the inverter circuit to carry out variable-speed driving. The inverter direct-current link voltage of the PWM voltage inverter circuit is set in correspondence with the terminal voltage of the permanent-magnet synchronous motor and the duty ratio of each switch of the bidirectional step-up/down converter circuit is selected. The output voltage of the accumulator is thereby increased or decreased to adjust the inverter direct-current link voltage to an appropriate value.