An active vibration insulator includes an electromagnetic actuator, a control-signals generating device, a driver, a calculator, and a judging device. The electromagnetic actuator generates vibrating forces depending on electric-current supplies. The control-signals generating device generates cyclic control signals based on cyclic pulsating signals output from a vibration generating source of a vehicle. The cyclic control signals actively inhibit vibrations generated by the vibration generating source from transmitting to a specific part of the vehicle. The driver drives the electromagnetic actuator by making the electric-current supplies variable based on the cyclic control signals. The calculator calculates an estimated transfer function composed of estimated values of a transfer function for a transfer system including the electromagnetic actuator and the driver. The judging device judges an inoperative malfunction of the electromagnetic actuator based the estimated transfer function.