This motor shaft state detection method has: a rotation determination step for determining, using a detected current waveform of a motor, whether or not to be a non-rotational state in which the rotational speed of the motor is smaller than a predetermined speed; a current determination step for determining whether or not to be a supply state in which the absolute value of current supplied to the motor is larger than a predetermined reference value; and a determination step for, when it is determined to be the non-rotational state in the rotation determination step and it is determined to be the supply state in the current determination step, determining that the motor is in a shaft locked state.