A failure diagnosis device comprising: an in-cylinder pressure sensor, disposed so as to face to the inside of a combustion chamber of an engine mounted on an automobile, and configured to output a signal corresponding to a pressure inside the combustion chamber; a fuel injection valve configured to supply fuel into the combustion chamber; an engine controller comprised of circuitry, into which a signal of one or more sensors (SW1-SW17) at least including the in-cylinder pressure sensor is inputted, and configured to operate the engine based on the signal of the one or more sensors (SW1-SW17); and a variable mechanism configured to change a valve timing of an intake valve, wherein the engine controller is configured to control the fuel injection valve according to an operating state of the engine, and diagnose a failure of the in-cylinder pressure sensor based on the signal of the in-cylinder pressure sensor, the engine controller is further configured to control the fuel injection valve to stop supply of fuel to the engine, when a fuel cut condition is satisfied while the automobile travels, limit an execution of the failure diagnosis of the in-cylinder pressure sensor until a given period has lapsed after the engine controller stops the supply of the fuel to the engine, and read the signal of the in-cylinder pressure sensor when the given period has lapsed after the engine controller stops the supply of the fuel to the engine, and diagnose the failure of the in-cylinder pressure sensor based on the read signal of the in-cylinder pressure sensor, and the engine controller is further configured to change the valve timing through the variable mechanism so that a close timing of the intake valve becomes a predefined target timing after stopping the fuel supply to the engine, and limit the execution of the failure diagnosis of the in-cylinder pressure sensor until the close timing of the intake valve becomes the target timing and the given period has lapsed, after the engine controller stops the supply of the fuel to the engine, wherein the given period is longer than a shortest change time required for the close timing of the intake valve becoming the target timing, and shorter than a longest change time required for the close timing of the intake valve becoming the target timing. an in-cylinder pressure sensor, disposed so as to face to the inside of a combustion chamber of an engine mounted on an automobile, and configured to output a signal corresponding to a pressure inside the combustion chamber; a fuel injection valve configured to supply fuel into the combustion chamber; an engine controller comprised of circuitry, into which a signal of one or more sensors (SW1-SW17) at least including the in-cylinder pressure sensor is inputted, and configured to operate the engine based on the signal of the one or more sensors (SW1-SW17); and a variable mechanism configured to change a valve timing of an intake valve, wherein the engine controller is configured to control the fuel injection valve according to an operating state of the engine, and diagnose a failure of the in-cylinder pressure sensor based on the signal of the in-cylinder pressure sensor, control the fuel injection valve according to an operating state of the engine, and diagnose a failure of the in-cylinder pressure sensor based on the signal of the in-cylinder pressure sensor, the engine controller is further configured to control the fuel injection valve to stop supply of fuel to the engine, when a fuel cut condition is satisfied while the automobile travels, limit an execution of the failure diagnosis of the in-cylinder pressure sensor until a given period has lapsed after the engine controller stops the supply of the fuel to the engine, and read the signal of the in-cylinder pressure sensor when the given period has lapsed after the engine controller stops the supply of the fuel to the engine, and diagnose the failure of the in-cylinder pressure sensor based on the read signal of the in-cylinder pressure sensor, and control the fuel injection valve to stop supply of fuel to the engine, when a fuel cut condition is satisfied while the automobile travels, limit an execution of the failure diagnosis of the in-cylinder pressure sensor until a given period has lapsed after the engine controller stops the supply of the fuel to the engine, and read the signal of the in-cylinder pressure sensor when the given period has lapsed after the engine controller stops the supply of the fuel to the engine, and diagnose the failure of the in-cylinder pressure sensor based on the read signal of the in-cylinder pressure sensor, and the engine controller is further configured to change the valve timing through the variable mechanism so that a close timing of the intake valve becomes a predefined target timing after stopping the fuel supply to the engine, and limit the execution of the failure diagnosis of the in-cylinder pressure sensor until the close timing of the intake valve becomes the target timing and the given period has lapsed, after the engine controller stops the supply of the fuel to the engine, wherein the given period is longer than a shortest change time required for the close timing of the intake valve becoming the target timing, and shorter than a longest change time required for the close timing of the intake valve becoming the target timing.