Water saving automatic valve

In a water saving automatic valve which is provided at water pipe and supplies water or blocks water, there is provided with a water saving automatic valve comprising a housing 4 which has a water line 2 inside and is connected to the water pipe, a motor 14 which is provided at the housing 4, a battery 20 which is connected to the motor 14 and supplies electric power, a screw shafts 8, 10 which are connected to the motor 14 and reciprocate with rotating, a diaphragm 6 which is connected to the screw shafts 8, 10 at the middle of the water line 2 of the housing 4 and opens or closes the water line 2 according as the screw shafts 8, 10 reciprocate, a sensor 50 which is connected the battery 20 and has a light emitter 50a as well as a light receptor 50b and controls the operation of the motor 14 by detecting approach of a user, and wherein the sensor 50 is operated in a certain pulse section because the light emitter 50a has a pulse generator 51 which is connected to the battery 20 and outputs a pulse and a bias controller 54 which is connected to the pulse generator 51 and transmits bias voltage synchronized with the pulse to the light receptor 50b and wherein the motor 14 is operated according to signal of the sensor 50 and the water line 2 is opened and closed according as the screw shafts 8, 10 are moved back and forth.