To provide a diagnosis function confirming device capable of reproducing failure mode and confirming a diagnosis function of an OBD system without necessitating replacement of failure parts and installing an another device into the OBD system directly.

This inspection device 30 for checking the OBD system 10 including a sensor 14 for detecting a condition of each part of a vehicle and an ECU 20 controlling each part of the vehicle and determining the presence or absence of failure based on the result of detection by a detection part has a connector 32 connected with the ECU 20 to transmit and receive a signal to/from the ECU and an inspection control part 36 transmitting a machining program 40 for rewriting data to be inputted and outputted into/from the ECU 20 to the ECU 20 through the connector 32 and giving an instruction to the machining program 40 in the ECU 20 through the connector 32 to rewrite data to be inputted and outputted into/from the OBD system.