A detector for an electromagnetic brake, for example used in an elevator system, that, by quantitative judgment, determines whether the brake force of the electromagnetic brake is appropriate. Load cells for detecting the recovery forces of brake springs are arranged between brake springs, which energize brake arms with brake shooes installed on them toward the side of brake wheel, and spring sheets, which hold brake springs in a compressive deformed state, and, at the same time, judgment part judges whether the brake force of electromagnetic brake 4 is outside a prescribed normal range based on the outputs of load cells. If the brake force of electromagnetic brake is outside the normal range, judgment part sends a signal, for example to a monitoring center.