To provide a mobile working device that downsizes the whole device and that can suck in chips or the like.

This device includes a circular saw 18 for cutting an object member, a hydraulic cylinder for moving the circular saw 18 in a working range, and a container chamber 24 for containing the saw 18 and moving together with the saw 18. The device also includes a fixing pipe 52 fixed having on opening portion over at least the moving range of the saw 18 and connected to the suck-in device. A belt member 56 is formed for blocking the opening portion of the pipe 52 and having a clear hole communicated with the containing portion 24 and moving on the opening portion of the pipe 52. The belt member 56 is a ring-like belt hang over between rollers 60 and 61 formed on both ends of the pipe 52.