The present invention relates to a drowsiness detection method. A heartbeat signal and a breathing signal are detected by exploiting together a scheme and an optical system scheme. The detected signals are applied to respective amplification units, noise signals are eliminated from the detected signals, and noise-free signals are amplified. The amplified signals are applied to a central processing unit, signal processing is processed on the signals, and processed signals are combined. The combined signal is counted, and a warning sound, voice message or vibration is output in a case where a value, obtained by subtracting a counted output value monitored one minute before a current time, from a counted output value monitored two minutes before the current time, falls within a detection range and where, with a passage of time, the value falling within the detection range is successively detected from two to ten times.