1. A system for estimating a self posture of a leg type moving robot controlled to follow a determined desired gait, comprising: a posture angular velocity detecting means for detecting or estimating an actual posture angular velocity of a predetermined part of the robot; an accelerometer mounted on the robot; a motional acceleration estimating means for determining an estimated motional acceleration as an estimated value of an acceleration of the accelerometer itself that is generated by a motion of the robot by using a motional state amount of the robot that includes at least one of a desired motion of the desired gait, a detected displacement value of a joint of the robot, and a desired displacement value of the joint; and a posture estimating means for estimating an actual posture of the predetermined part on the basis of at least a detected acceleration value by the accelerometer, the estimated motional acceleration, and the detected or estimated actual posture angular velocity.