To prohibit lifting of a jack in a condition other than the condition in which the jack can be lifteed stably.

In a jack-up device of a construction machine provided with a plurality of jack-up cylinders 5 which take the attitude at which they are erected in a substantially vertical condition for the ground surface when jack lifting work is done and take the storage attitude at which they are tilted for a vertical condition when jack lifting work is not done drive means 31, 34 which expand, shrink, and drive a plurality of jack-up cylinders 5, a detection means SW1 which detects the presence of the cylinder 5 which does not take the erection attitude among a plurality of cylinders 5 and outputs a drive impossible signal and a prohibition means 33 which prohibits the drive of the cylinders 5 by the drive means 31, 34 when the drive impossible signal is output from the detection means 21.