An electric machine controlling method for executing either one of a current vector control and a voltage phase control such that supply power to an electric machine is controlled in accordance with an operating state of the electric machine, the controlling method comprising a voltage phase control step of calculating a voltage command value (v dv_fin *, v qv_fin *) for the voltage phase control based on a voltage norm command value (V a *) indicative of a magnitude of a supply voltage to the electric machine and a voltage phase command value (a*) indicative of a phase of the supply voltage, wherein the voltage phase control step includes: a state amount calculation step of calculating a state amount (Φ 0_est) of either one of magnetic flux generated in the electric machine and a parameter correlated to the magnetic flux, based on a current (id, iq) supplied to the electric machine; and a norm change step of changing the voltage norm command value (V a *) in accordance with the state amount (Φ 0_est), the method being characterized by: a switching step of, in a case where a control on the electric machine is switched from the current vector control to the voltage phase control, switching the control on the electric machine to the current vector control when a command value correlation parameter correlated to the voltage norm command value (V a *) or the voltage norm command value is lower than a predetermined voltage threshold (V a_th1), wherein: the command value correlation parameter includes at least one of a value obtained by performing an averaging process on the voltage norm command value (V a *), a norm component of the voltage command value (v d_fin *, v q_fin *), and a value obtained by performing the averaging process on the norm component of the voltage command value (v dv_fin *, v qv_fin *), and the predetermined voltage threshold (V a_th1) is a value smaller than an upper limit (V a_max) of the voltage norm command value (V a *). a voltage phase control step of calculating a voltage command value (v dv_fin *, v qv_fin *) for the voltage phase control based on a voltage norm command value (V a *) indicative of a magnitude of a supply voltage to the electric machine and a voltage phase command value (a*) indicative of a phase of the supply voltage, wherein the voltage phase control step includes: a state amount calculation step of calculating a state amount (Φ 0_est) of either one of magnetic flux generated in the electric machine and a parameter correlated to the magnetic flux, based on a current (id, iq) supplied to the electric machine; and a norm change step of changing the voltage norm command value (V a *) in accordance with the state amount (Φ 0_est), a state amount calculation step of calculating a state amount (Φ 0_est) of either one of magnetic flux generated in the electric machine and a parameter correlated to the magnetic flux, based on a current (id, iq) supplied to the electric machine; and a norm change step of changing the voltage norm command value (V a *) in accordance with the state amount (Φ 0_est), the method being characterized by: a switching step of, in a case where a control on the electric machine is switched from the current vector control to the voltage phase control, switching the control on the electric machine to the current vector control when a command value correlation parameter correlated to the voltage norm command value (V a *) or the voltage norm command value is lower than a predetermined voltage threshold (V a_th1), wherein: the command value correlation parameter includes at least one of a value obtained by performing an averaging process on the voltage norm command value (V a *), a norm component of the voltage command value (v d_fin *, v q_fin *), and a value obtained by performing the averaging process on the norm component of the voltage command value (v dv_fin *, v qv_fin *), and the predetermined voltage threshold (V a_th1) is a value smaller than an upper limit (V a_max) of the voltage norm command value (V a *). the command value correlation parameter includes at least one of a value obtained by performing an averaging process on the voltage norm command value (V a *), a norm component of the voltage command value (v d_fin *, v q_fin *), and a value obtained by performing the averaging process on the norm component of the voltage command value (v dv_fin *, v qv_fin *), and the predetermined voltage threshold (V a_th1) is a value smaller than an upper limit (V a_max) of the voltage norm command value (V a *).