To provide a safety cover device of a circular sawing machine surely opening/closing a safety cover for protecting a disc saw of the circular sawing machine by a simple mechanism.

A center of an approximately sectorial safety cover 14 is swingably supported on a pivot shaft 14a positioned to displace from a rotation center of the disc saw 11 on a cutting blade casing 12 covering the disc saw 11 except a working part 12a. A tip of a control lever 15 is coupled with a working pin 14b planted in the vicinity of an end 14c of an arc of the cover. A base end of the control lever 15 is rotatably supported on a spindle 13a of a working lever 13 having one end coupled with the cutting blade casing 12. A stopper plate 18 is provided, which stops the swing of the control lever 15 while the disc saw 11 turns from a retreat position to a cutting position by the swing of the lever 13. The safety cover 14 opens a working area 12a by the swing of the lever 13 after the control lever 15 stops, and a paper pipe C is cut by the cutting blade of the disc saw 11 exposed on the working area 12a.