A master electronic control device for a vehicle is provided as follows. A vehicle time, which is managed by the master electronic control device to be used in common with a slave electronic control device, is transmitted to the slave electronic control device. Device log information is received from the slave electronic control device, the device log information including (i) a content of an event in the slave electronic control device, (ii) a device time in the slave electronic control device when the event is detected, and (iii) information on vehicle time reception state. The device time included in the device log information is converted into the vehicle time that corresponds to the device time in response to that the information on vehicle time reception state indicates that, when the event is detected, the slave electronic control device has not received the vehicle time.