PURPOSE: To contrive extension of life of a blade, by a method wherein only pure water is fed to the blade by interrupting feed of carbon dioxide between a first wafer cutting process and second wafer cutting process.

CONSTITUTION: A device 1 is constituted of a pure water feed device 2, a, cutting-off device having a blade 5, a detecting device 12 detecting a wafer 10 on a mount 9 and a device 13 controlling feed of carbon dioxide by providing them. The control device 13 mixes the carbon dioxide into the pure water only when the blade 5 is dicing the wafer 10. As the control device 13 does not feed the carbon dioxide when the blade 5 is not dicing, a period of time when the blade is exposed into acid water and etched is shortened and shortening of life of the blade 5 can be prevented.