A module electric tool comprises a lower cover including receiving compartments and a receiving cavity formed therein, an upper cover engaged with the lower cover, an gear box module received in the receiving compartment and including a rotary stem disposed at the front end thereof and an input sleeve mounted at the rear end thereof; an motor module received in the receiving compartment and including a driving shaft affixed at the front end thereof and electrical contacts formed on the rear end surface thereof, an electrical switch module received in the receiving compartment and including electrical contacts fixed at the front and rear ends thereof, respectively, and a press button attached at the peripheral side thereof, a battery module fitted in the receiving cavity and including electrical contacts provided at the front end thereof for couplingly contacting with the electrical contacts of the electrical switch module, thus obtaining an assembled convenience and lowering the production cost.