Abstract: A drainpipe cleaning apparatus prevents leakage of cleaning fluid from the drainpipe while cleaning the drainpipe. The drainpipe cleaning apparatus 1 has a cleaning fluid tank 10 for storing the cleaning fluid, a fluid delivery line 15, fluid drain line 23, gas-liquid separation tank 24, gas exhaust line 26, circulation line 28, gas recovery line 31, cleaning fluid return line 33, and control device 45. The control device 45 runs a cleaning process by driving a gas discharge pump 36 to create negative pressure inside the wastewater drainpipe 2 in a transit vessel and driving a cleaning fluid pump 16 to cause the cleaning fluid to flow backwards through the wastewater pipe 2. The control device 45 also monitors the pressure detected by a inlet-side pressure detector 20 during the cleaning process.