A maintenance system of a vehicle comprising: a server device; a terminal device; wherein the terminal device is configured to transmit a maintenance command to an in-vehicle device; and the in-vehicle device installed in a vehicle, wherein the server device includes: a worker authentication information reception unit configured to receive worker authentication information from the terminal device; a server authentication processing unit configured to perform an authentication process on the worker authentication information; and a server key transmission unit configured to transmit a first key to be used with the in-vehicle device to the terminal device whose worker authentication information has been successfully authenticated by the server authentication processing unit, wherein the terminal device includes: a worker authentication information transmission unit configured to transmit the worker authentication information to the server device; a terminal key reception unit configured to receive the first key from the server device; and a terminal authentication processing unit configured to perform an authentication process with the in-vehicle device using the first key; characterized in that the terminal device further includes: a terminal key storage unit configured to store the first key received from the server device; and a terminal control unit configured to cause the first key to be erased from the terminal key storage unit by a signal indicating an end of maintenance work on the vehicle, and wherein the in-vehicle device includes a vehicle authentication processing unit configured to perform an authentication process with the terminal device using the first key. a server device; a terminal device; wherein the terminal device is configured to transmit a maintenance command to an in-vehicle device; and the in-vehicle device installed in a vehicle, wherein the server device includes: a worker authentication information reception unit configured to receive worker authentication information from the terminal device; a server authentication processing unit configured to perform an authentication process on the worker authentication information; and a server key transmission unit configured to transmit a first key to be used with the in-vehicle device to the terminal device whose worker authentication information has been successfully authenticated by the server authentication processing unit, a worker authentication information reception unit configured to receive worker authentication information from the terminal device; a server authentication processing unit configured to perform an authentication process on the worker authentication information; and a server key transmission unit configured to transmit a first key to be used with the in-vehicle device to the terminal device whose worker authentication information has been successfully authenticated by the server authentication processing unit, wherein the terminal device includes: a worker authentication information transmission unit configured to transmit the worker authentication information to the server device; a terminal key reception unit configured to receive the first key from the server device; and a terminal authentication processing unit configured to perform an authentication process with the in-vehicle device using the first key; characterized in that the terminal device further includes: a terminal key storage unit configured to store the first key received from the server device; and a terminal control unit configured to cause the first key to be erased from the terminal key storage unit by a signal indicating an end of maintenance work on the vehicle, and a worker authentication information transmission unit configured to transmit the worker authentication information to the server device; a terminal key reception unit configured to receive the first key from the server device; and a terminal authentication processing unit configured to perform an authentication process with the in-vehicle device using the first key; characterized in that the terminal device further includes: a terminal key storage unit configured to store the first key received from the server device; and a terminal control unit configured to cause the first key to be erased from the terminal key storage unit by a signal indicating an end of maintenance work on the vehicle, and a terminal key storage unit configured to store the first key received from the server device; and a terminal control unit configured to cause the first key to be erased from the terminal key storage unit by a signal indicating an end of maintenance work on the vehicle, and wherein the in-vehicle device includes a vehicle authentication processing unit configured to perform an authentication process with the terminal device using the first key.