Magnetic tape casette with reel brake mechanism

A tape is provided with a reel brake and a tape-protecting lid of the cassette. This tape-protecting lid has side plates, parallel to the side walls of the cassette housing extends, and pivotally mounted on the side wall, reel brake mechanism has a brake plate, releasable position and a braking position of the brake freely between, and is biased toward the braking position. A side wall provided between the housing and the reel brake plate means for holding engagement with each other between the reel brake plate and the side wall, thereby protecting the engagement between the two, with the tape-protecting lid open automatically release the brake.