PROBLEM TO BE SOLVED: To retract a front end side pendant in a desired folded state.SOLUTION: An operation support device 28 includes: a target angle storage section 30 for storing a first target angle for an interior angle between a boom and a jib and a second target angle of a smaller interior angle therebetween; a controller 33; and an instruction output section 34 for outputting an operation instruction in response to a command from the controller 33. The controller 33 causes output of an instruction for grounding the front end part of the jib at the first target angle when the tilting operation of a front attachment from a working state can be stably carried out at the first target angle. When the operation is unstable, the boom is lowered to form the first target angle on the ground after the front end of the jib is grounded at the second target angle, and then the controller 33 causes output of an instruction for tensioning a front end side pendant. This can always place the front attachment into a state in which the front end of the jib is grounded at the first target angle and the front end side pendant is tensioned. Then, the controller 33 causes output of an instruction for operation to make the boom and the jib horizontal.