A posture computing apparatus for a work machine is an apparatus that obtains a posture angle of a work machine including a traveling body and a swing body that is mounted on the traveling body and that rotates relative to the traveling body. The posture computing apparatus includes a detection apparatus that is provided to the swing body and detects angular velocity and acceleration; an acceleration correcting unit that corrects the acceleration detected by the detection apparatus, based on a position where the detection apparatus is placed and information on the detection apparatus; and a posture angle computing unit that obtains a posture angle of the work machine from the acceleration corrected by the acceleration correcting unit and the angular velocity detected by the detection apparatus.