To secure the supporting force of any hydraulic jack affected by regulation when jack-up operations have been completed while the telescopic driving of one or two hydraulic jacks is left as is regulated in a hydraulic jack automatic horizontal set-up device for a mobile type crane.

In this hydraulic jack automatic horizontal set-up device provided with a hydraulic control means 2, an inclination detection means 3, and with an electrical signal processing circuit 4, in which the device is so constituted that a high order side jack extension regulating signal for regulating the extension drive of each hydraulic jack at the high order side of a vehicle concerning inclination, is outputted by the electrical signal processing circuit 4, supporting force detection means 17a through 17d are mounted to hydraulic jacks 1a through 1d respectively, and concurrently, detected signals from them are inputted to the electrical signal processing circuit 4. When the supporting force of any applicable hydraulic jack is found to have been lower than a specified value, in case the high order side jack extension regulating signal is outputted, the high order side jack extension regulating signal is thereby discontinued.