An endoscope cleaning/disinfecting apparatus, comprising: a processing tank having a concave shape and including an opening portion which opens upward; an apparatus main body which performs processing using liquid on an endoscope arranged in the processing tank; a lid member which is disposed so as to be movable between a sealing position at which the opening portion is sealed and an open position at which the opening portion is open; a sealing member which is sandwiched between the lid member and the processing tank in a state where the lid member is located at the sealing position, and which is configured to improve a sealing property of the opening portion by the lid member; an electric actuator which is connected to the lid member and which generates a pressing force for pressing the lid member toward the opening portion; and a control section connected to the apparatus main body and electrically connected to the electric actuator, the control section controlling the apparatus main body and the driving of the lid member so as to cause the lid member to locate at the sealing position by actuating the electric actuator and thereafter cause the processing to be executed, wherein the processing includes a process in which the liquid is introduced into the processing tank, characterized in that the control section causes the electric actuator to continue to generate a pressing force for pressing the sealing member by the lid member toward the opening portion in a predetermined period during execution of the processing, and causes the electric actuator to stop generating the pressing force in a period other than the predetermined period during the execution of the processing, and wherein the predetermined period during the execution of the processing includes a period in which a liquid surface in the processing tank is located higher than a position at which the sealing member and the processing tank are in contact with each other. a processing tank having a concave shape and including an opening portion which opens upward; an apparatus main body which performs processing using liquid on an endoscope arranged in the processing tank; a lid member which is disposed so as to be movable between a sealing position at which the opening portion is sealed and an open position at which the opening portion is open; a sealing member which is sandwiched between the lid member and the processing tank in a state where the lid member is located at the sealing position, and which is configured to improve a sealing property of the opening portion by the lid member; an electric actuator which is connected to the lid member and which generates a pressing force for pressing the lid member toward the opening portion; and a control section connected to the apparatus main body and electrically connected to the electric actuator, the control section controlling the apparatus main body and the driving of the lid member so as to cause the lid member to locate at the sealing position by actuating the electric actuator and thereafter cause the processing to be executed, wherein the processing includes a process in which the liquid is introduced into the processing tank, characterized in that the control section causes the electric actuator to continue to generate a pressing force for pressing the sealing member by the lid member toward the opening portion in a predetermined period during execution of the processing, and causes the electric actuator to stop generating the pressing force in a period other than the predetermined period during the execution of the processing, and wherein the predetermined period during the execution of the processing includes a period in which a liquid surface in the processing tank is located higher than a position at which the sealing member and the processing tank are in contact with each other.