A red light and an infrared light which are emitted from a light emitting portion 2 are transmitted through a fingertip 4 of a subject and are converted into electric signals by a light receiving portion 3. The respective signals are separated and amplified and are then sent to a CPU 8. In the CPU 8, the input signals are divided into D.C. components DC1 and DC2 and A.C. components AC1 and AC2, changes &Dgr;A1=(AC/DC) 1 and &Dgr;A2=(AC/DC)2 in an absorbance are calculated, high frequency components thereof are extracted, a mutual ratio &PSgr; is calculated, and a noise removing waveform is calculated based thereon. Based on the noise removing waveform, a pulse wave is detected, a pulse rate is calculated, a display wave form is calculated and an oxygen saturation is calculated. These are displayed through a display unit 11.