In an environment inspection mode of a calibration system, a radar device executes a signal analysis process to calculate an eigenvalue ratio of each comparison eigenvalue. The eigenvalue ratio has a small value when a pair of eigenvalues corresponding to arrival radar waves has a strong correlation. On the other hand, the eigenvalue ratio has a large value when the eigenvalue ratio is calculated between an eigenvalue and thermal noise. When there is no eigenvalue which is not more than a reference threshold value, the radar device indicates a notice that the current environment is suitable for the calibration of the radar device. On the other hand, when there is presence of at least one eigenvalue of not more than the reference threshold value, the radar device indicates a notice that the current environment is unsuitable for the calibration of the radar device.