A seat belt alarm apparatus according to the present invention executes a weak alarm pattern in which an alarm lamp is blinked and lighted repeatedly when a seat belt switch is turned on and a seat belt is unfastened, and a vehicle speed is equal to or less than a buzzer sound start vehicle speed. When the vehicle speed is more than the buzzer sound start vehicle speed, the seat belt alarm apparatus executes a strong alarm pattern in which the alarm lamp is blinked and lighted repeatedly as well as a buzzer is sounded in synchronism with the blinking of the alarm lamp, and the alarm operation is continued until the seat belt switch is turned off and the seat belt is fastened.