The sleep diagnosis device 1 of the present invention comprises three-dimensional acceleration sensors 2a and 2b, a posture detector 5 which detects a posture of the patient from a DC component of the three-dimensional acceleration sensors, and a breathing movement detector 4 which detects a breathing movement of the patient from the AC component of the three-dimensional acceleration sensors. The sleep diagnosis device of the present invention can detect the posture (sleeping posture) and the breathing movement of the patient by using one three-dimensional acceleration sensor, so it is possible to reduce the number of sensors. Furthermore, the sleep diagnosis device can detect the breathing movement accurately by the three-dimensional acceleration sensors.