A positioning device for assembling parts on a structure is disclosed. The controller also includes a voltage command value calculation processing means which calculates a voltage command value based on the first and second electric current command values and an adjusting value calculation processing means for calculating an adjusting value of the first electric current command value and for performing weak field control based on the voltage command value. The chlorate aqueous solution and acidic substances are quickly injected into the well by an injection pump, so they react with each other and produce chlorine dioxide.