Provided are a synchronous machine control device SMCD including a converter configured to boost a voltage of a direct current power source DCPS in which, when the SMCD returns to operation after the operation stopping, fail-proof return to operation through the prevention of damage to the DCPS and the shortening of the time required for the return to operation are balanced. When returning to operation, the SMCD issues an operation enable command to an inverter and the converter simultaneously in the case where a calculated electric power value calculated from a rotational speed and a torque command is equal or higher than a threshold and, in the case where the calculated electric power value is less than the threshold, issues an operation enable command to the converter after an operation command that makes the electric power of the inverter equal or higher than a threshold is issued.