In this way, as shown in FIG. 1, in the case in which an object to be cleaned 3 such as a tank is conveyed into the prescribed position inside the pedestal 2 via the conveyor 4, first, the drive cylinder 7 is driven to lower the whole internal cleaning apparatus 1 together with the outer pipe 14, causing the nozzle 29 portion to enter the interior of the internal space 51 of the object to be clean