1. A behavior analysis device comprising: an object extraction portion that processes a frame image of an imaging area being imaged by an imaging device and extracts an object being imaged; a position detection portion that detects a position in the imaging area, for each object extracted by the object extraction portion; a posture estimation portion that estimates a posture of the object, for each object extracted by the object extraction portion; and a behavior determination portion that determines a behavior of the object, for each object extracted by the object extraction portion, based on the position in the imaging area that is detected by the position detection portion and the posture estimated by the posture estimation portion wherein the posture estimation portion, for each object extracted by the object extraction portion, sets up a rectangular area surrounding the object and estimates the posture of the object based on a ratio between a height of the rectangular area and a width of the rectangular area, a height of an upper side of the rectangular area, and a height of a lower side of the rectangular area.