A refrigerator comprising: a compressor, and a motor driving device used for the compressor, the motor driving device comprising: a brushless DC motor that drives a load that fluctuates during one rotation; a driver that applies a voltage to the brushless DC motor and drives the brushless DC motor; a speed accelerator that accelerates the brushless DC motor, a position detector that detects a magnetic pole position of the brushless DC motor, and a speed detector that calculates a current driving speed of the brushless DC motor from the position detected by the position detector, characterized in that the speed accelerator is configured to determine the voltage to be applied by the driver so as to maintain a speed change rate of a speed within one rotation from start of the brushless DC motor with respect to a speed calculated by the speed detector at a next one rotation within a predetermined value or less, wherein the speed accelerator is configured to maintain the speed change rate of the speed within one rotation from the start of the brushless DC motor with respect to the speed calculated by the speed detector at the next one rotation within the predetermined value or less under a condition where a change of the load during one rotation is maximized, wherein, in a state of performing positioning the driver is further configured to flow a current to a specific phase of the brushless DC motor before start of the motor driving device, and further configured to flow a current to a phase advanced by 90 degrees or more from the phase positioned after lapse of a predetermined time, the driver is configured to acquire position information of the position detector, and to start to drive the motor driving device, wherein the compressor is configured to start in a state where a pressure difference remains between a suction side and discharge side of the compressor. a compressor, and a motor driving device used for the compressor, the motor driving device comprising: a brushless DC motor that drives a load that fluctuates during one rotation; a driver that applies a voltage to the brushless DC motor and drives the brushless DC motor; a speed accelerator that accelerates the brushless DC motor, a position detector that detects a magnetic pole position of the brushless DC motor, and a speed detector that calculates a current driving speed of the brushless DC motor from the position detected by the position detector, characterized in that the speed accelerator is configured to determine the voltage to be applied by the driver so as to maintain a speed change rate of a speed within one rotation from start of the brushless DC motor with respect to a speed calculated by the speed detector at a next one rotation within a predetermined value or less, wherein the speed accelerator is configured to maintain the speed change rate of the speed within one rotation from the start of the brushless DC motor with respect to the speed calculated by the speed detector at the next one rotation within the predetermined value or less under a condition where a change of the load during one rotation is maximized, wherein, in a state of performing positioning the driver is further configured to flow a current to a specific phase of the brushless DC motor before start of the motor driving device, and further configured to flow a current to a phase advanced by 90 degrees or more from the phase positioned after lapse of a predetermined time, the driver is configured to acquire position information of the position detector, and to start to drive the motor driving device, wherein the compressor is configured to start in a state where a pressure difference remains between a suction side and discharge side of the compressor. a brushless DC motor that drives a load that fluctuates during one rotation; a driver that applies a voltage to the brushless DC motor and drives the brushless DC motor; a speed accelerator that accelerates the brushless DC motor, a position detector that detects a magnetic pole position of the brushless DC motor, and a speed detector that calculates a current driving speed of the brushless DC motor from the position detected by the position detector, characterized in that the speed accelerator is configured to determine the voltage to be applied by the driver so as to maintain a speed change rate of a speed within one rotation from start of the brushless DC motor with respect to a speed calculated by the speed detector at a next one rotation within a predetermined value or less, wherein the speed accelerator is configured to maintain the speed change rate of the speed within one rotation from the start of the brushless DC motor with respect to the speed calculated by the speed detector at the next one rotation within the predetermined value or less under a condition where a change of the load during one rotation is maximized, wherein, in a state of performing positioning the driver is further configured to flow a current to a specific phase of the brushless DC motor before start of the motor driving device, and further configured to flow a current to a phase advanced by 90 degrees or more from the phase positioned after lapse of a predetermined time, the driver is configured to acquire position information of the position detector, and to start to drive the motor driving device, wherein the compressor is configured to start in a state where a pressure difference remains between a suction side and discharge side of the compressor.