Abstract: A casing for a magnetic tape cassette capable of constantly actuating a slider with high reliability for a long period of time, even under conditions of high temperature. The casing includes a casing body having an upper casing member and a lower casing member joined together, and a tapping boss of high rigidity arranged therein, with a slider being slidably mounted on the lower casing member so as to cover at least a part of a bottom and sides of the lower casing member. The casing also includes a torsion spring arranged in the casing body to act on the slider, the torsion spring having a coil-like portion supported on a supporting member mounted on the lower casing member, and an end of the torsopm spring engaged with the slider. The other end of the torsion spring is securely held in an engagement portion formed at the tapping boss.

Abstract: A magnetic tape cassette having a protective slide cover for a space between a front portion of the cassette and a pivotal front lid covering a magnetic tape exposed at the front portion. Forward end of the slide cover is provided with a projection adapted to engage the front lid to prevent the cover from deformation.