Abstract: A brushless d.c. motor is equipped with a stator armature, which is composed of a stator yoke and at least one armature coil arranged on the stator yoke, and a 2p(p: a positive integer of 1 or more)-pole magnetic rotor facing the stator armature, rotatable relative to the stator armature and having alternating N and S poles. The motor can self-start by utilizing a cogging torque produced upon feeding a direct current to a position sensor. The stator yoke defines at such a point as permitting self-starting of the magnet rotor a cut-off portion of such a shape that ensures the self-starting of the magnet rotor and provides an ideal composite torque curve. The brushless d.c. motor enjoys easy assembly work, low manufacturing cost, compact size, good performance, good mass productivity, etc. It is suited particularly as a disk-type brushless motor or disk-type burshless fan motor.