speed of a crankshaft not shown an accelerator opening degree sensor 30 detects an accelerator opening degree which corresponds to a depressed amount of an accelerator pedal not shown an atmospheric pressure sensor 31 is installed on a vehicle not shown and detects an atmospheric pressure sensor values obtained by these sensors 29 to 31 are supplied to the ecu 40 which is electrically connected to the sensors 29 to 31 the ecu 40 performs various types of control such as control over fuel injection for the engine 10 and includes a cpu a rom a ram input ports output ports and other elements which are known in the art in addition the ecu 40 includes an intake air temperature calculation unit 42 a sensor output value calculation unit 44 and an intercooler diagnosis unit 45 as functional components thereof it is assumed in the following description that all of these functional components are included in the ecu 40 which is a single piece of hardware but one or more of these functional components may be included in a separate piece of hardware the intake air temperature calculation unit 42 is an example of a fluid temperature calculation unit according to the present invention and calculates the temperature of the intake air on an upstream side of the intercooler 16 i e between the compressor.