An electric power tool includes a tool unit and a battery pack. The tool unit includes a pair of conjunct grooves and two corresponding blocks. The battery pack includes a pair of conjunct rails and two locking members. The tool unit and the battery pack are connected and locked with each other respectively by that the conjunct grooves and the conjunct rails are interconnected with each other and the two locking members and the two blocks are jammed together. In addition, the tool unit and the battery pack can be dimensionally reduced and the cohesive effect therebetween can be strengthened respectively by the conjunct grooves and the conjunct rails.