Abstract: A diagnostic data collection unit (10) that collects diagnostic data of a vehicle is connected to electronic control units (11) and (12) for the vehicle through a CAN, and includes a specifying device for measurement items that specifies the measurement items to the electronic control units (11) and (12), a recording device (24) for diagnostic data that records control data based on the specified measurement items and operating data of each apparatus sent from the electronic control units (11) and (12), and a storage device (25) for recorded data that stores the recorded data of the recording device for the diagnostic data of during a predetermined period before or after a trigger generating device is activated.