A luggage door unlocking device for a vehicle, capable of unlocking the luggage door of the vehicle without using an unlocking key includes a portable signal transmitter for transmitting an unlocking signal; signal receiving device provided on the vehicle, for receiving and discriminating the unlocking signal; and a driving device which drives an unlocking mechanism on the basis of the received and discriminated unlocking signal. The signal receiving device has a magnetic sensor, a smoothing circuit which smoothes the reception signal provided by the magnetic sensor and provides a smoothed signal, and a comparator which receives the reception signal and the smoothed signal and allows the reception signal to pass only when the signal level of the reception signal changes beyond the signal level of the smoothed signal. The noise overlapping the reception signal is eliminated by the comparator, whereby an unlocking signal including no noise is fed to the driving device.