An engine ECU compares an acceleration value with a reference value, which corresponds to an accelerator operation value inputted in response to a user operation on an accelerator pedal, and stores vehicle behavior data when the acceleration value exceeds the reference value. After determining that the acceleration value is larger than the reference value and storing the vehicle behavior data, the reference value is changed to a larger value. After determining that the acceleration value is smaller than the reference value and, for example, a period in which the acceleration value remains lower than the reference value, reaches a set period, the reference value is changed to a smaller value. Thus, the number of times of storing the vehicle behavior data is equalized among vehicle users.