Vehicle exterior images are captured sequentially by an imaging portion of an imaging-equipped mobile terminal used in a first vehicle and stored temporarily in an image temporary-storage portion in the first vehicle. The first vehicle receives vehicle information from a second vehicle different from the first vehicle, through inter-vehicle communication. When it is determined that a sudden deceleration arises in the second vehicle based on the vehicle information received by the first vehicle, the vehicle exterior images stored in the image temporary-storage portion are read and saved in a memory.