A luggage door unlocking device for a vehicle by which a luggage door of vehicle can be unlocked without using an unlocking key is disclosed. The device includes a portable transmitter for generating an unlocking signal, a receiver which is mounted on a vehicle for receiving and discriminating the unlocking signal when the transmitter approaches the receiver and a luggage door unlocking mechanism for operating an unlocking mechanism of the vehicle when the receiver receives the unlocking signal. The transmitter has a walk detector for detecting the periodical vibrations when the person carrying the transmitter is walking which generates a walk detecting signal. Also, a switch turns on or off upon receiving the walk detecting signal from the walk detector. In the luggage door unlocking device, the transmitter having the switch which is turned off upon receiving the walk detecting signal, the transmitter begins to generate the unlocking signal just after the person carrying the transmitter stops walking so that the luggage door is automatically unlocked just after he stops walking.