In the present invention, constructed is a highly reliable system that does not allow unforeseen conditions to occur in the remote diagnosis of a clamp device. All combinations of status of a state detection switch mounted on a clamp device are anticipated in advance by a recursive method, and the states are defined with no omissions. A control unit 9 includes: a main body memory 9c that stores the ON/OFF state of a state switch together with the status of an injection molding machine main body, the clamp status and time information; and a main body communication unit 9d which is capable of short-range wireless communication. A message diagnosing a failure is stored in a smartphone 12 for all combinations of the ON/OFF state of the state detection switch for each of the following cases: whether in mold replacement mode or not; and whether a clamp device is in a clamped state or an unclamped state, or in a state other than the forgoing. The history of the ON/OFF state of the state detection switch with respect to the status of the main body and the clamp status is read from the main body memory 9c by wireless communication, and a corresponding message is displayed.