Drainage pipe cleaning device etc. in which leakage of cleaning liquid from a drainage pipe can be prevented. The drainage pipe cleaning device comprises a cleaning liquid tank for containing cleaning liquid, a liquid feeding pipe , a liquid discharge pipe , a gas/liquid separation container , a discharge pipe , a circulation pipe , a gas recovery pipe , a cleaning liquid return pipe , and a controller . The controller performs cleaning operation where the inside of the drainage pipe in a mobile machine body is set to negative pressure by means of a gas discharge pump and the cleaning liquid is caused to flow back into the drainage pipe by means of a liquid feeding pump . Also, the controller monitors a pressure level detected by a pressure detector during the cleaning operation, and when the pressure level exceeds the atmospheric pressure, the controller performs cleaning liquid recovery operation to recover the cleaning liquid in the drainage pipe into the cleaning liquid tank through the liquid feed pipe and the cleaning liquid return pipe , where the cleaning liquid recovery operation is performed by stopping the liquid feed pump , closing a delivery valve , opening acleaning liquid return valve , opening an open valve , and closing a gas recovery valve .