To provide a posture controlling device in a working machine capable of maintaining a set posture of a working part relatively to a ground by suitably detecting the posture of the working part capable of freely changing its posture relatively to the ground relative to the machine body part, without installing a complicated and expensive facility on the ground side.

This posture controlling device in a working machine can obtain a posture of the machine body part as GPS posture data of a time series with a prescribed time interval based on a double phase difference obtained from both carrier wave information of a GPS standard station on the ground and a GPS receiving means on the working machine side, and also a changed amount of the position of the machine body part as posture data of an inertia navigation in the time series by an inertia navigation calculating part INS based on the information of an inertia navigation detecting part S5, S6. The working part is maintained at a set posture relatively to a ground by changing its posture relative to the machine body part, based on the information of the detected posture of the machine body relative to the ground at the current time obtained from GPS posture data at the time by a set time interval before the current time and inertia navigation posture data at the current time and a detected information on the posture of the working part relative to the machine body part.