A misuse detection method used in an electronic control unit in a vehicle network system including multiple electronic control units that communicate with one another through networks. The misuse detection method includes receiving a target data frame at one time point, and receiving a reference data frame at another time point different than the one time point. The misuse detection method further includes performing, as misuse detection for the target data frame based on a certain rule specifying a reception interval between the one time point at which the target data frame is received and the other time point at which the reference data frame is received, and determining the target data frame received is for misuse based on a length of the reception interval.