Abstract: A cutting machine for cutting a flat cardboard plate 2 includes first and second rotary cutters 7 and 8 rotatable in respective directions counter to each other for cutting upper and lower portions of a thickness of the flat cardboard plate 2, respectively. The first and second rotary cutters 7 and 8 and the flat cardboard plate 2 are moved relative to each other in a direction conforming to a single cutting line b to cut the flat cardboard plate 2 along the cutting line b. In this way, the flat cardboard plate 2 having a relatively great thickness can be cut with high cutting accuracy.