To notify a user of a cause of incorrect detection of a brain wave detection signal, which is caused by at least the reduction or the like of the outside air temperature.

The biological information detecting device 1 includes a brain wave detecting part 4 attached on a user for detecting a brain wave signal of the user, and the SN condition of the brain wave signal is detected. It is determined that whether the SN condition is better or worse than the predetermined reference condition, and when the SN condition is not better than the reference condition, it is determined that whether the temperature around the brain wave detecting part 4 is lower or not than the reference temperature. In the case of the lower temperature around the brain wave signal detecting part 4 than the reference temperature, the device is adapted to report to an annunciation part 55 that the brain wave signal cannot correctly be detected because the temperature around the brain wave signal detecting part 4 is lower than the predetermined reference temperature.