Embodiments of the invention provide a magnetic recording and reproducing apparatus that allows a mounting space for an electric signal wiring to be sufficiently secured relative to a circuit board and the circuit board to be secured stably to the case. In one embodiment, a case having a built-in head disk assembly includes board fixing bodies disposed in a protruding condition at two of four corners thereof. Protruding ends of the board fixing bodies include fit grooves. A circuit board for drivingly controlling the head disk assembly is fitted into the fit grooves in the board fixing bodies.