The present invention discloses a device for measuring physiological data of a subject. It comprises a light modulation unit, an optical detection unit and a signal processing unit. The present invention can operate in an active mode or a passive mode to measure a subject's heart rate, respiratory information, haemoglobin level, cardiac output or oxygen saturation of the blood, etc. Fourier Transform based lock-in technique is used to detect the physiological signals reliably even when the signal is weak. In addition, ambient light can be used as the light source to complete the measurement.