Abstract

A safety device for a crane which can make a safety operation precisely taking a relationship between a swinging condition of a boom and a limit working region into consideration. In the device, a working radius and a swinging angle of the boom and projection amounts of projectable support members of the crane are detected, and a limit working region of the boom is set in accordance with a weight of a suspended cargo and the projection amounts. A remaining angle over which the boom can be swung until the set limit working region is exceeded is calculated, and also a braking angular acceleration at which swinging movement of the boom is braked and stopped without leaving a shake of the suspended cargo is calculated. Further, a swinging angle of the boom required to brake and stop the swinging movement of the boom at the braking angular acceleration is calculated, and the thus calculated required angle and the remaining angle are compared with each other. Thus, a safety operation is performed before the remaining angle exceeds the required angle. Meanwhile, the set limit working region and a current working radius and swinging angle of the boom are indicated on the same screen of a display unit.