PURPOSE: To enhance the measuring precision of a heart rate measuring device suitable for use in judging the lowering of awakining degree of a driver, without a detection error by enabling it to judge the inherent waveform pattern generated with heart rate, and to output the heart rate information.

CONSTITUTION: The electric potential difference between both hands of a driver is measured continuously by means of electrodes 1a, 1b of a cardiac muscle activity electric potential measuring means 6 mounted on a steering handle of a vehicle, and the waveform of electric potential difference obtained is sent to an A/D conversion part 5 as the waveform of cardiac muscle activity electric potential through processing in an amplifier part 2, low pass filter 3, etc. A signal of cardiac muscle activity electric potential data after A/D conversion is stored in a judging means 7 for every specified time, and continuous rising or lowering is judged from the stored data lines, then it is judged whether the waveform of continuous rising or lowering is inherent in heart rate or not. When the ratio between accumulative addition values of continuous rising or lowering is in a specified range, it is judged that the waveform pattern is one inherent generated by heart rate.