A method for detecting an initial position of a rotor of a permanent magnet synchronous motor in a no-load environment can comprise the steps of: estimating a temporary initial position α′ by means of aligning a d axis; measuring a first voltage command which is output by performing velocity control within predetermined velocity ranges with respect to the forward direction of a motor on the basis of the temporary initial position α′; measuring a second voltage command which is output by performing velocity control within the predetermined velocity range with respect to the reverse direction of the motor on the basis of the temporary initial position α′; calculating respective variations of the first voltage command and second voltage command, and calculating a compensation angle α″; and calculating an initial position α of the rotor on the basis of the sum of the temporary initial position α′ and compensation angle α″.