PROBLEM TO BE SOLVED: To implement acquisition of a posture during sleeping by using a non-contact and small-sized device.SOLUTION: A biological information acquisition device irradiates a subject during sleeping with a micro wave and takes in data obtained by detecting the micro wave reflected by the subject (50)； divides the data on the basis of timing when the subject's body moves (54)； extracts a breathing component and heartbeat component from the individual divided data (56 to 62)； and sets a posture determination threshold (66). The biological information acquisition device determines apnea when extracting no breathing component (72), determines that the subject is on the back when average amplitude Pbreath of the breathing component is larger than a posture determination threshold T(76), determines that the subject is on the stomach when the average amplitude Pbreath is equal to or larger than a posture determination threshold T(T<；T) (80), determines that the subject is on the right side when the average amplitude Pbreath is smaller than the posture determination threshold Tand average amplitude Pheart of the heartbeat component is larger than a posture determination threshold T(84), and determines that the subject is on the left side when the average amplitude Pbreath is smaller than the posture determination threshold Tand the average amplitude Pheart of the heartbeat component is equal to or smaller than the posture determination threshold T(86).
