An equipment monitoring system having a detector configured to detect a physical quantity of a monitored equipment, wherein the monitored equipment is a steam trap, and a diagnosis unit configured to diagnose an operating state of the monitored equipment based on detection results by the detector, the equipment monitoring system comprising: a control unit configured to switch a detection operation mode of the detector between a simple detection mode and a detailed detection mode, the modes having different operation times of the respective detection operations; wherein in the simple detection mode, the detector is configured to periodically perform the detection operation, the detection operation having a shorter operation time than the operation time of the detailed detection mode, and in the detailed detection mode, the detector is configured to continuously perform the detection operation, for a predetermined time period the detection operation having a longer operation time than the operation time of the simple detection mode, wherein the diagnosis unit is configured to, in the simple detection mode, diagnose whether the operating state of the monitored equipment is a normal state or a state requiring caution based on the detection results by the detector, and wherein the diagnosis unit is configured to, in the detailed detection mode, repeatedly diagnose whether the operating state of the monitored equipment is the normal state or the state requiring caution based on the detection results by the detector in the predetermined time period, and the control unit is configured to, in the simple detection mode, when the diagnosis unit has diagnosed the operating state of the monitored equipment to be the normal state, maintain the simple detection mode, and when the diagnosis unit has diagnosed the operating state of the monitored equipment to be the state requiring caution, switch the detection operation mode of the detector from the simple detection mode to the detailed detection mode and when, in the detailed detection mode, the operating state of the monitored equipment is diagnosed to be the estate requiring caution for a predetermined consecutive number of times in a repetition, the diagnosis unit is configured to diagnose that the operating state of the monitored equipment is an abnormal state. a control unit configured to switch a detection operation mode of the detector between a simple detection mode and a detailed detection mode, the modes having different operation times of the respective detection operations; wherein in the simple detection mode, the detector is configured to periodically perform the detection operation, the detection operation having a shorter operation time than the operation time of the detailed detection mode, and in the detailed detection mode, the detector is configured to continuously perform the detection operation, for a predetermined time period the detection operation having a longer operation time than the operation time of the simple detection mode, wherein the diagnosis unit is configured to, in the simple detection mode, diagnose whether the operating state of the monitored equipment is a normal state or a state requiring caution based on the detection results by the detector, and wherein the diagnosis unit is configured to, in the detailed detection mode, repeatedly diagnose whether the operating state of the monitored equipment is the normal state or the state requiring caution based on the detection results by the detector in the predetermined time period, and the control unit is configured to, in the simple detection mode, when the diagnosis unit has diagnosed the operating state of the monitored equipment to be the normal state, maintain the simple detection mode, and when the diagnosis unit has diagnosed the operating state of the monitored equipment to be the state requiring caution, switch the detection operation mode of the detector from the simple detection mode to the detailed detection mode and when, in the detailed detection mode, the operating state of the monitored equipment is diagnosed to be the estate requiring caution for a predetermined consecutive number of times in a repetition, the diagnosis unit is configured to diagnose that the operating state of the monitored equipment is an abnormal state.