A driving device for a permanent magnet synchronous motor, the driving device comprising: a current command generation unit configured to output a current command value based on a torque command value; a voltage command generation unit configured to output a voltage command value for driving a permanent magnet synchronous motor based on the current command value; and a magnet information estimation unit configured to estimate a magnetic flux quantity of a magnet or a temperature of a magnet that is included in the permanent magnet synchronous motor, characterized in that the driving device is configured to provide a period in which: the torque command value is zero before the torque command value is raised, in coasting restart, due to starting a voltage output to the permanent magnet synchronous motor from a state in which a voltage output to the permanent magnet synchronous motor is stopped and the rotor of the permanent magnet synchronous motor is free-run, a current command value on a q-axis is set to zero, and a current command value on a d-axis is set to a predetermined value other than zero; and the magnet information estimation unit is configured, based on the voltage command value and rotation speed information on the permanent magnet synchronous motor in said period, to estimate the magnetic flux quantity of the magnet included in the permanent magnet synchronous motor or the temperature of the magnet. a current command generation unit configured to output a current command value based on a torque command value; a voltage command generation unit configured to output a voltage command value for driving a permanent magnet synchronous motor based on the current command value; and a magnet information estimation unit configured to estimate a magnetic flux quantity of a magnet or a temperature of a magnet that is included in the permanent magnet synchronous motor, characterized in that the driving device is configured to provide a period in which: the torque command value is zero before the torque command value is raised, in coasting restart, due to starting a voltage output to the permanent magnet synchronous motor from a state in which a voltage output to the permanent magnet synchronous motor is stopped and the rotor of the permanent magnet synchronous motor is free-run, a current command value on a q-axis is set to zero, and a current command value on a d-axis is set to a predetermined value other than zero; and the torque command value is zero before the torque command value is raised, in coasting restart, due to starting a voltage output to the permanent magnet synchronous motor from a state in which a voltage output to the permanent magnet synchronous motor is stopped and the rotor of the permanent magnet synchronous motor is free-run, a current command value on a q-axis is set to zero, and a current command value on a d-axis is set to a predetermined value other than zero; and the magnet information estimation unit is configured, based on the voltage command value and rotation speed information on the permanent magnet synchronous motor in said period, to estimate the magnetic flux quantity of the magnet included in the permanent magnet synchronous motor or the temperature of the magnet.