To solve a problem of causing countless disasters such as various falls, service interruption and crashes by the looseness of bolts and nuts due to insufficient fastening or a failure to fasten the bolt and nut in conventional washers which have no indication of fastening torque of bolts and nuts nor any indication for the failure to fasten them.

The washer is characterized in that fastening pressure is applied to the washer by fastening with suitable fastening torque and that the pressure range is color-coded into a plurality of fastening pressure ranges. A method for determining from the obvious state when there is insufficient fastening or a failure to fasten can be solved by using this washer.