To provide a function for assuring circulation of an etchant by effectively removing the gas, generated from the etchant, from within an injection line and an injection pump, while using a pump of blade water pump type which does not cause pulsation to be generated in injection pressure at low cost.

A control device 9 opens shielding valves 5A and 6A, to activate an injection piping 2A and an injection pump 3A, and circulates an etchant in an etching bath 1 by using an injection line A. If a drop in the flow rate of the etchant is observed by analyzing the signal from a flow rate sensor 4, the control device 9 closes the shielding valves 5A and 6A, stops the injection piping 2A and the injection pump 3A; whereas, it opens shielding valves 5B and 6B to activate an injection piping 2B and an injection pump 3B so that the etchant is circulated by an injection line B. Under the condition with the injection line A being stopped, a gas release valve 8A is opened, and the gas is released in the injection piping 2A and the injection pump 3A.