An endoscope cleaning/disinfecting apparatus for cleaning/disinfecting an endoscope (51, 52), the apparatus comprising: an endoscope connection portion (24a to 24h) connectable to a duct of the endoscope (51, 52); a fluid feeding duct including one end connected to the endoscope connection portion (24a to 24h); a flow measurement section configured to measure a flow of a liquid supplied from the endoscope connection portion (24a to 24h) to the endoscope (51, 52); a liquid supply duct including one end connected to another end of the fluid feeding duct, and another end connected to a liquid supply source; a pump provided in the liquid supply duct, the pump being configured to make the liquid stored in the liquid supply source flow from the other end of the liquid supply duct toward the endoscope connection portion (24a to 24h); a first atmospheric exposure duct including one end connected to the fluid feeding duct and another end exposed to atmosphere; and a relief valve disposed at an intermediate position of the first atmospheric exposure duct, the relief valve being configured to open upon application of a pressure that is equal to or exceeds a predetermined pressure from the one end toward the other end of the first atmospheric exposure duct, a control section configured to control driving of the pump and to determine clogging of the endoscope duct when a decreased flow is measured by the flow measurement section; characterized by a first stop section disposed at an intermediate position of the first atmospheric exposure duct, the first stop section being configured to open/close the first atmospheric exposure duct; and the control section configured to control opening/closing of the first stop section, and when detection of clogging of the duct of the endoscope (51, 52) is performed using the flow measurement section, the control section being configured to close the first stop section and to drive the pump to supply the liquid into the duct of the endoscope (51, 52), wherein in the first atmospheric exposure duct, the relief valve is disposed on the fluid feeding duct side relative to the first stop section. an endoscope connection portion (24a to 24h) connectable to a duct of the endoscope (51, 52); a fluid feeding duct including one end connected to the endoscope connection portion (24a to 24h); a flow measurement section configured to measure a flow of a liquid supplied from the endoscope connection portion (24a to 24h) to the endoscope (51, 52); a liquid supply duct including one end connected to another end of the fluid feeding duct, and another end connected to a liquid supply source; a pump provided in the liquid supply duct, the pump being configured to make the liquid stored in the liquid supply source flow from the other end of the liquid supply duct toward the endoscope connection portion (24a to 24h); a first atmospheric exposure duct including one end connected to the fluid feeding duct and another end exposed to atmosphere; and a relief valve disposed at an intermediate position of the first atmospheric exposure duct, the relief valve being configured to open upon application of a pressure that is equal to or exceeds a predetermined pressure from the one end toward the other end of the first atmospheric exposure duct, a control section configured to control driving of the pump and to determine clogging of the endoscope duct when a decreased flow is measured by the flow measurement section; characterized by a first stop section disposed at an intermediate position of the first atmospheric exposure duct, the first stop section being configured to open/close the first atmospheric exposure duct; and the control section configured to control opening/closing of the first stop section, and when detection of clogging of the duct of the endoscope (51, 52) is performed using the flow measurement section, the control section being configured to close the first stop section and to drive the pump to supply the liquid into the duct of the endoscope (51, 52), wherein in the first atmospheric exposure duct, the relief valve is disposed on the fluid feeding duct side relative to the first stop section.