Abstract: An automatic flush device is provided that is mounted in a water tank. The automatic flush device includes an inlet control module, a lever module for discharging water and a tank module. The inlet control module includes an inlet element linked to the inlet tube and a solenoid valve set at the inlet element. The lever module for discharging water has a cup connected with the solenoid valve by a filling tube. An electronic sensing controller controls the opening and closing of the solenoid valve to fill water into the cup. When the cup is full of water, the lever unbalances and slants to control the flushing of the water tank. Therefore, it is easy to control water current while requiring minimal power, thereby saving electric energy.