A drilling device includes an end cutting tool, a main housing, a motor, a transmission, and a dust collection unit. The end cutting tool processes a workpiece. The motor is provided in the main housing for generating a torque. The transmission transmits the torque to rotate the end cutting tool. The dust collection unit collects dust generated by the rotation of the end cutting tool. The dust collection unit includes a dust case for accumulating the dust therein. The dust case is detachable from the main housing and having an inlet and an outlet. The inlet and the outlet are oriented in a single direction.