PURPOSE: To realize a bubble detecting and erasing device with high speed and high efficiency, by arranging a permalloy detector at both sides to be orthogonal to a bubble transfer pattern and providing a detecting area for the permalloy detector.

CONSTITUTION: When a bubble extending current pulse is applied to a hair pin shaped conductor 3 for a bubble B1 or B2 transferred along a bubble transfer pattern 1, the bubble is extended along the inside of the conductor pattern 3. Since a permalloy detector 4 is arranged in crossing with the pattern 1, an output is generated at the extension of the bubble, and the direction of the bubble extension goes to upper and lower two directions, the time required for the extension can be halved. Further, since a detecting area 2 with a limited size is provided for a part of the detector 4, the floating magnetic flux from the extended bubble can effectively be exerted to the detector 4. The erase of bubbles can be realized by appling a reverse current pulses.