To provide a motor-driven nailing machine capable of realizing miniaturization, compactification, weight-reduction, and cost-reduction by reducing the number of components.

The motor-driven nailing machine 1 is composed by including a housing 2, a plunger 13 for driving a nail with reciprocation in the housing 2, a supporting roller 15 for supporting the plunger 13, an outer rotor (a motor) 16 for driving the plunger 13, a rotor (a driving roller) rotationally driven by the outer rotor 16, and a moving means (a linear motor 23 and an arm 25) for making the outer rotor 16 or the supporting roller 15 contact with or separate from the plunger 13 by moving the outer rotor 16 or the supporting roller 15.