PURPOSE: To provide an automatic measuring instrument for supplied water for automatically calibrating a water pressure measurement value.

CONSTITUTION: In an automatic measuring instrument for supplied water where a room is separated into a water quality measurement room and an electrical control room and a water quality instrumental meter detection part and a pipe for measurement are installed at the water quality measurement room and, a sequencer, a touch panel, and a data transmission part, etc., are installed in the electrical control room, a solenoid value 11 in normally-open state is installed at the entrance of a water pressure measurement system pipe and a solenoid valve 12 in normally-closed state is installed at the exit side. The ON/OFF of the valves 11 and 12 is controlled by a sequencer. The pressure measurement signal of a pressure measuring instrument 1A is inputted to the sequencer 3, data which are subjected to operation processing are used for data transmission, etc., to the display of a touch panel 4 or a center. With the calibration of the pressure measurement value, a measurement value in the state that the water pressure measurement system pipe is released into atmosphere is used as a reference value and the reference value is subtracted from the normal measurement value, and then the operation is performed by the sequencer.