An offset number setting device that freely and easily sets an offset number for a tool to be mounted on a tool holder of a turret surface. A display linkage unit displays a turret surface selection screen on a display, displays a tool holder selection screen on the display by selecting the turret surface, and displays an offset number setting screen on the display by selecting the tool holder. An offset number is therefore set for the tool along with the selection of the turret surface on which the tool is mounted.