A magnetic disc recording and/or reproducing apparatus in which a magnetic disc cassette containing a magnetic disc provided with a center hub is loaded so that the center hub engages with a rotary shaft of a disc rotating motor to rotate the magnetic disc. A cam for displacing a magnetic head is fitted to the outer periphery of a boss supporting a bearing which supports rotatably the rotary shaft, so that the force from the cam can be transmitted to the magnetic head through a bearing utilizing the rotational movement having a high transmission efficiency. As a result, a pulse motor for displacing the magnetic head can be made compact in size and light in weight and the power consumption of the pulse motor can be reduced. The cam is interposed between the level of the magnetic head and the chassis and the rotary shaft of the disc rotating motor is used also as the rotation center for the cam via a bearing mechanism, so that the magnetic head can access any position. As a result, a positioning mechanism can be disposed in a small space, so that the magnetic disc recording and/or reproducing apparatus can be made in compact in size and light in weight.