Abstract: A working machine which is intended for demolishing and excavating work comprises a chassis, an upper part carried by said chassis and arranged for rotational movement relative thereto about a vertical axis, and an arm arrangement carried by the upper part and including a jib structure which is connected at one end thereof to the upper part and the other end of which carries, via an intermediate arm, a fitting for a tool, such as an excavator bucket, a chiseling device or like tool. The jib structure and the intermediate arm are connected to the upper part and to each other respectively via pivots and can be pivoted in a vertical plane by means of first and second pressure piston-cylinder devices active between the upper part and the jib structure and between the jib structure and the intermediate arm respectively. The jib structure is divided into a first, short jib section which is pivotally connected to the upper part, and a second, longer jib section which is pivotally connected to the first jib section.