Abstract: A thermistor layer of the present invention is configured to be disposed in an electrical current path. The thermistor layer comprises a thermosensitive particle, a plurality of electro-conductive particles covering a surface of the thermosensitive particle, and a binder adhering the electro-conductive particles, the electro-conductive particles form an electro-conductive network, at least the surface of the thermosensitive particle is made of a thermoplastic resin, the thermoplastic resin softens at a temperature lower than a temperature at which the binder softens, and the thermistor layer is provided to become highly resistive due to softening and deformation of the thermoplastic resin.

Abstract: A magnetic disk cassette that has a slidable shutter with a first notch, the shutter being open by engaging a swingable shutter opener with the first notch while the magnetic disk cassette is being inserted into a cassette holder, wherein single or plural second notches are provided at a portion of the cassette that is symmetrical to the position of the first notch with respect to the rotation center of a magnetic disk that is housed in the cassette, whereby when the cassette is inserted into the cassette holder up side down, the shutter opener engages with the second notch(es) to prevent the cassette from being inserted to the innermost of the cassette holder.