PURPOSE: To provide a simple chemical liquid injection control unit which is applicable to the size reduction of a water tank while allowing the frequent intermittent pumping operation of a lifting pump.

CONSTITUTION: This chemical liquid injection control unit CC is equipped with an operation means SW which is connected between power lines L and N and the lifting pump PW and stops the lifting pump PW when the water level in the water tank reaches a certain value, a timer means which clocks the operation time of the lifting pump PW, and a control means having a holding means which holds the clocked time quantity of the timer means when the operation of the lifting pump PW is stopped, and places a chemical liquid injection pump PC interlockingly with the lifting pump PW when the time clocked quantity reaches a certain value.