A magnetic recording/reproducing apparatus is provided with a lock releasing arm for depressing a lock releasing switch on a front cover of a cassette. The magnetic recording/reproducing apparatus uses a cassette positioning means for positioning a cassette until the cassette is automatically inserted, including the lock releasing arm having a claw to be in contact with a side wall on a cassette inserting direction side of a hole where the lock releasing switch is provided, and a projection to be in contact with the front face of the cassette when the cassette is inserted. When the cassette is brought into contact with the projection, the lock releasing arm depresses the lock releasing switch to position the cassette.