A corrugated paperboard box making machine, which includes: a slotter for slotting a corrugated paperboard sheet to form slots; a die-cutter disposed downstream of the slotter, the die-cutter including a die cylinder with a punching die and an anvil cylinder; a cutting blade for cutting, in cooperation with the anvil cylinder, the corrugated paperboard sheet slotted by the slotter, into two small-size corrugated paperboard sheets, along a direction perpendicular to the conveyance direction; and a displacement mechanism for displacing the cutting blade as to allow the cutting blade to be selectively set in a cutting position and a non-cutting position.