To provide an outrigger extending amount detecting device detecting an outrigger extending amount without arranging a detector having a mechanical structural part in an outrigger so as to solve problems that the detector composed of a limit switch or a potentiometer needs to be arranged in the outrigger for detecting the outrigger extending amount, such detector has the mechanical structural part and operation failure of the structural part might cause breakdown, which decreases the reliability.

A vehicle 1 with a working machine mounted therein has outriggers 8 respectively arranged to projected to front/rear/left/right directions of the vehicle 1 for supporting the vehicle 1. The device detects the extending amounts of the outriggers 8 by monitoring cameras 21 for shooting the outriggers 8 and image recognition means 22 for recognizing the projecting amounts of the outriggers 8 from images shot by the monitoring cameras 21.