To provide a dosimeter suitable for dissipating user's anxiety.

A prediction device 100 includes: a prediction unit 102 which predicts the occurrence of a natural phenomenon which suddenly changes a measured value or an indicated value of a personal dosimeter 210; and a transmission unit 104 which transmits a prescribed notification to the personal dosimeter 210 via the Internet 199 when the occurrence of a natural phenomenon is predicted by the prediction unit 102. The personal dosimeter 210 includes: a measurement unit 212 for measuring a radiation dose; a display unit 214 for displaying radiation dose information based on the radiation dose measured by the measurement unit 212; a reception unit 218 for receiving the prescribed notification from the prediction device 100; and a prediction notifying unit 220 which, on reception of the prescribed notification by the receiving unit 218, notifies that the change of the measured value or the indicated value of the personal dosimeter 210 may be caused by the natural phenomenon.