To provide a new method to surely improve sharpness of a kitchen knife simply using a file plate and (water resistant) paper file by even an amateur, and a cutting board with the file plate and the (water resistant) paper file.

This method to improve sharpness of the kitchen knife is very simple for the amateur, and the sharpness is overwhelmingly improved just only by inclining the kitchen knife at an appropriate angle and lightly stroking on the file plate 2a, or (water resistant) paper file 2b in the right or left direction for several times. The file plate 2a or the (water resistant) 2b is attached to the cutting board 1.