A brushless DC motor is provided and includes: a stator assembly; a rotor assembly including a sleeve; a case assembly; and a circuit board assembly which has an electronic component mounted thereon. The case assembly is provided with an opening, the electronic component passes through the opening so as to protrude inside the case assembly, and a groove is formed at an axial end of the sleeve of the rotor assembly in order to prevent the electronic component from making contact with any part of the rotor assembly. Thus, the axial dimension of the brushless DC motor that includes the electronic component disposed to protrude inside the case assembly can be successfully reduced in such a manner that the electronic component is accommodated within the groove. Further, no electronic component is disposed around the outer circumference of the stator assembly and therefore the radial dimension also can be kept small.