A safety device for power window comprises a storage unit for storing the pulse width change rate of continuous pulses detected by a pulse width detector during a window glass raising operation at a reference timing, a calculation unit for calculating the pulse width change rate of continuous pulses detected by the pulse width detector during a window glass raising operation at an operational timing and a control unit for comparing the stored value of a pulse width change rate with the calculated value of a pulse width change rate and driving a motor for raising/lowering window glass in a window opening direction when a total of differences between the both pulse change rates exceeds an allowable value.