PURPOSE: To prolong the lifetime of a water environment measuring sensor by dipping the measuring sensor only when the measurement of water environment is necessary.

CONSTITUTION: A valve opening signal 151a is delivered from a control element 150 to a valve operating element 123, an air vent valve 122 is opened and water W is introduced into a tubular body 120. When a time required for a water environment measuring sensor 110 to be dipped in the water W passes, subsequently, a valve closing signal 151b is delivered from the control element 150 to the operating element 123. At the same time, a measurement start signal 152a is delivered to the sensor 110 and a result 110a of measurement is delivered from the sensor 110. Then, a measurement end signal 152b is delivered to the sensor 110 and a pump start signal 153a to an air press-in pump 140 respectively. Receiving the signal 152b, the sensor 110 ends the measurement of water environment, while the pump 140 starts to press air into the tubular body 120. As the pressing-in proceeds, an internal pressure of the tubular body 120 rises and the water W staying inside the tubular body 120 is discharged from a water introduction port 121.