A monitor which can detect respiration of a sleeping person without being affected by the attitude of the sleeping person or the indoor illumination light and can easily evaluate detected respiration quantitatively through image measurement. The monitor comprises means (1) for projecting a specified illumination pattern, means (5) for picking up the image of projected light continuously, means (7) for calculating inter-frame moving amount of the illumination pattern from the image of two frames acquired by the image pickup means at different times, means (8) for generating a moving amount waveform data comprising inter-frame moving amounts arranged in time series, and means (9) for detecting the movement of an object from the moving amount waveform data.