A torque control method for permanent magnet synchronous motor (PMSM) in flux weakening region has been proposed. However in particular case, current control response of proposed method becomes oscillatory. Therefore, stable operating condition is analyzed in this paper. It is revealed that the gain of transfer function from feedback component of voltage phase angle to actual q-axis current is increased in the high frequency region close to the resonant frequency. It is revealed that the ratio of d-axis and q-axis stator windings linkage flux should be considered for the stable operation because it affects the q-axis current control performance. The revealed stable operating condition is verified by experimental test with 1kW class IPMSM.