An acceleration detector has a case and a movable magnetic body mounted in the case and supported by a leaf spring secured to the case. The magnetic body is thus movable in either of two opposite directions in response to acceleration. Stoppers made of a magnetic material protrude from an inner surface of the case to locations adjacent both ends of the magenetic body, with predetermined gaps left therebetween. Two pairs of primary and secondary coils are provided around the magnetic body for producing a difference in induced voltages output by the secondary coils according to the displacement of the magnetic body. A yoke made of soft magnetic material extends from the case to location adjacent the magnetic body.