A seatbelt reminder system warns a crew member when the crew member has not fastened a seatbelt. The system makes a way of giving a reminder different between a case (S302, S303, or S304) where the running state of a vehicle is detected when the unfastened state of the seatbelt is detected and a case (S310, S311, or S312) where the unfastened state of the seatbelt is detected when the running state of the vehicle is detected.