PURPOSE: To prevent a detergent from drooping from a nozzle by providing a return pipe for communicating the leading path of a pump and the tank of soap liquid while being branched to an injection pipe, and further, providing the difference in height between the lower end of the return pipe and the nozzle.

CONSTITUTION: An air sucking pipe 6 for which a silencer 11 is fitted to the top end, liquid leading pipe 13 for which a stop valve 12 is fitted to the top end, and leading path 14 for leading out air mixed liquid prepared by mixing a liquid-state detergent 1 and air with the rotational force of a pump 3 are connected to the pump 3, and an injecting pipe 16 and a return pipe 17 communicated into a tank 2 storing the liquid-state detergent 1 are connected through a mesh cylinder 15 for foaming to the leading path 14. A nozzle 4 is fitted at the top end of a drooping part 16C of the injecting pipe 16, and the large difference in height is provided between the lower end of the return pipe 17 and the nozzle 4 as much as possible.