PURPOSE: To eliminate uneven portions of deflection up to about 0.03 mm from a circular saw blade plane by disposing a feeler gauge at the same distance from the center point of the circular saw blade within a regular angle range relative to straightening rollers.

CONSTITUTION: When a dial gauge 26 encounters an uneven portion of deflection above a preset limit value in a saw blade 1, an incremental generator 7 helps to determine the time that corresponds to the distance from the dial gauge 26 to straightening rollers 14 and 14'. After this determined time, a control unit 11 feeds signals into straightening units in straightening stations 8 and 9 to drive air cylinders 16 or thus rotate axes 13 such that the straightening rollers 14 and 14' paired with lower rollers 17 and 17' are pressurized appropriately to flatten the uneven portion of the saw blade 1. A protrusion of the uneven portion needs one straightening roller 14' depressed, while a depression needs the other straightening roller 14 depressed.