PURPOSE: To automatically make unlocked state when a battery is used up by method in which an urgent holding type electromagnet to operate locker in preference to the usual holding type electromagnet and a sensor to watch the consumption of battery are provided, and when the consumption of battery is increased unlocking state is produced automatically.

CONSTITUTION: An electronic lock is provided with a bolt 1, an unusually using magnetic holding type electromagnet 4, a permanent magnet 5, a movable iron piece 7 for unlocking, a sensor 11 to detect the position of the piece 7, an usually using magnetic holding type electromagnet 12, CPU 17, and a sensor 18 for the voltage of battery. When a battery 19 is consumed, the drop of voltage is detected by the sensor 18, and electric current is sent to the magnet 4 through a switch circuit 20 by CPU 17 to weaken the holding force of the magnet 5. When the force of the spring 6 is increased, the piece 7 is clockwise turned and a hook 8 is released to make unlocked state. During the period when the battery is consumed, unlocking is automatically made to avoid becoming the opening of door impossible.