To enable a stable use in an outrigger one side overhang state.

A boom 6 is arranged via a turntable 5 on a vehicle body 1 having outriggers 2L, 3L and 2R, 3R. A circular arc plate 11 of a shape of extending at a central angle of 1/2 of a boom turning maximum allowable angle in the outrigger one side overhang state to both sides in the circumferential direction with the turning axis as the center, is arranged from a just under position of the boom 6 in an outer peripheral part of the turntable 5. Detectors 12A and 12B facing near to both ends of the circular arc plate 11 when arranging the boom 6 toward the rear of a vehicle body, are arranged on the vehicle body 1. When selecting a work state on the right side of the vehicle body 1 by a work performing side selection switch, by boom turning controller, only left turn is permitted when both detectors 12A and 12B are ON, lateral turn is permitted when the detector 12A is ON and the detector 12B is OFF, and only right turn is permitted when both detectors 12A and 12B are OFF.