A compact ball tap with 1 a water level switch which comprises a guide standpipe 5 vertically arranged in a tank T, a float 6 slidably installed on the guide standpipe 5, a valve 3, a lever 4 controlling an open-close action of the valve 3 connected with the float 6, and a water level switch 29 transmitting predetermined control signals when the float 6 shifts to a predetermined water level, wherein one float 6 is shared by the ball tap 1 and the water level switch 29.