To provide a circular saw cutter capable of efficiently cutting a work without being conscious of decrease in diameter due to abrasion and re-grinding of a circular saw blade.

In this circular saw cutter, saw heads 11 to 13 where circular saw blades 17 to 19 are mounted are moved by a driving means with a controller 30 to thereby cut a work. A detecting means (touch sensor 20 to 22) for detecting the arrival of outside diameter parts of the circular saw blades 17 to 19 are disposed in a part of moving areas of the circular saw blades 17 to 19. The outside diameter sizes of the circular saw blades 17 to 19 are computed according to the central position information on the circular saw blades 17 to 19 obtained from the controller 30 when the arrival of the outside diameter parts of the circular saw blades 17 to 19 is detected and automatically input to the controller 30.