To provide a system capable of accurately displaying the cleaning timing and the replacing timing of a cooling means, by improving diagnostic accuracy of cooling capacity of the cooling means, in a controller temperature diagnostic system.

This controller temperature diagnostic system has an environmental temperature detecting means 5 for detecting the environmental temperature outside a controller 3, an inside temperature detecting means 13 for detecting the inside temperature in the controller 3, a temperature difference arithmetic operation means 15 for arithmetically operating a temperature difference between the respectively detected inside temperature and environmental temperature, a temperature rise theoretical value arithmetic operation means 15 for arithmetically operating a temperature rise theoretical value of the controller 3 from a calorific value by heating parts 16 to 19, and a diagnostic means 15 for diagnosing the cooling capacity of the cooling means 14 on the basis of the respectively arithmetically operated temperature difference and temperature rise theoretical value.