1. A motion detection apparatus for detecting a position and a posture of an object to be measured, comprising: an inertia motion detecting section which detects an inertia motion of the object to be measured by using at least one of an acceleration sensor and an angular velocity sensor; an image pickup section, which is fixed to the inertia motion detecting section, which picks up a peripheral image of the object to be measured; an image comparing section which compares images picked up at different points in time by the image pickup section; a camera position and posture acquiring section which detects a position and a posture of the object to be measured by using a result of comparing the images by the image comparing section; and a spatial position and posture acquiring section which detects a position and a posture in space of the object to be measured on the basis of information obtained by the inertia motion detecting section and the camera position and posture acquiring section.