Moveable working device with supporting extension arms

The invention relates to a working device, comprising an undercarriage (10), two front and two rear supporting extension arms (22,24) which can be extended from a travel position into at least one support position, which can be supported on a foundation (36) through a supporting leg (28), also provided with a respective measuring member (38) for determining the support load acting upon the supporting legs; and a device for monitoring the stability comprising a computer-assisted evaluation electronics system to supply to support load measurement values of all supporting legs in the predetermined scanning period; a software routine is provided for stability control in order to determine a stability figure which is determined on the basis of the quotients of the overall sum of the support load measurement values of all supporting legs and a partial sum of the support load measurement values of the two supporting legs which are momentarily subjected to a support load. An alarm routine is also provided in order to