A cabin is formed as a casing body partitioned and separable from a vehicle body and includes an air purifier for introducing purified air into the casing body to maintain the pressure inside the cabin at a positive level by the air purifier. When the lockup clutch is in the lockup state, a variation of a generated torque is detected. In addition or alternatively, prior to anonymization of the log entries, session identifications are assigned to identified groups of log entries.