Cassette lid-locking element with shutter portion for closing a light passage window

A magnetic tape cassette, which comprises a tape cassette housing, a lid provided at a front face of said tape cassette housing pivotally supported by side walls of said tape cassette housing for selectively opening and closing an opening portion of said magnetic tape cassette to draw out a magnetic tape incorporated therein, and a lid-locking stopper member for retaining said lid in a closed state pivotally supported by at least one of said side walls of said magnetic tape cassette, whereby said opening portion is closed thereby;

• said tape cassette housing having detecting windows for tape end detection in said side walls thereof, said lid-locking stopper member including a stopper portion for maintaining said lid in said closed state to close said opening portion, a releasing operating portion for releasing said lid from said closed state, and a detecting window open/close portion for protecting said tape end detecting windows from the environment when in said closed state and retaining said tape end detecting windows open upon release of said lid from said closed state.