When an engine load QC is equal to or larger than a predetermined value, an acceleration-state determiner determines that a turbine is in an acceleration state, and a supercharging-pressure-control-state determiner determines that supercharging-pressure controller (a bypass valve, a wastegate, and a variable flap) of a turbocharger are in a maximum supercharging pressure control state (a closed valve state), i.e., when a delay coefficient α of the turbocharger calculated by a delay-coefficient calculator on the basis of an actual supercharging pressure πc and a convergent value πc* of a supercharging pressure calculated by a convergent-value calculator indicates a value peculiar to the turbocharger, a failure of the supercharging-voltage controller is determined on the basis of the delay coefficient α. Thus, it is possible to secure a high failure detection accuracy, and increase a frequency of performing failure detection even when the engine load QC suddenly changes to cause a delay in a response of the supercharging pressure πc.