PURPOSE: To bypass a driving current with a switch when a driving pulse width or a duty cycle reaches a prescribed value or over, by monitoring a driving time of a functional element of a magnetic bubble element and providing a switch operated basing on this monitor.

CONSTITUTION: A function criving dircuit FD responds to a pulse signal s1, turns on a transistor TR1, and flows a pulse current which is determined with a power supply voltage V0, resistor r0 of the function element and a limit resistor r1, to the function element r0. A pulse time monitor circuit PTS is operated to turn on a short-circuit switch SW when a signal with a pulse width wider than a specified pulse width is inputted or a pulse train having a specified duty and over is inputted. When a transistor (TR)TR2 of the switch SW is activated, a current flowing to the function element is switched to a bypass consisting of a diode d1 and the TR2, allowing to prevent an abnormal current from flowing to the function element.