To sufficiently wash a mixer large in volume equipped with a plurality of kneading shafts using a small capacity pump as it is and to miniaturize a washing apparatus while reducing a production cost.

This mixer washing apparatus is equipped with a nozzle insertion port 12 for inserting a nozzle 11 into a kneading tank 2, a pipe shaft 24 having the nozzle provided to the leading end thereof and supplying high pressure water to the nozzle, a pipe shaft extending mechanism 22 for allowing the pipe shaft to advance and retreat axially and allowing the nozzle to advance into and retreat from the kneading tank, a pipe shaft shaking mechanism 18 for shaking the pipe shaft forwardly and rearwardly in such a state that the nozzle is inserted into the kneading tank, a sealing mechanism 41 for sealing the nozzle insertion port in such a state that the nozzle is inserted into the kneading tank, a closing means 14 for closing the nozzle insertion port in such a state that the nozzle is retracted and a control means for controlling the movements of the pipe shaft extending mechanism, the pipe shaft shaking mechanism and the closing means.