To provide a locking washer almost never loosening up and screws with locking washers attaching the same.

This locking washer 1 has two or more legs 7 at a lower part of a cylinder shape or an umbrella shape washer. The legs are compressed when they are pressed against a matter to be fastened by fastening of the screws, restoration force is accumulated. The washer 2 is pressed against a head part back surface of the screws and a fastening member by restoration force, makes a bolt and nut not easily rotate in reverse direction and not loosen up easily. A fitting projection formed on the washer fits in a fit in socket part of the bolt and the nut to regulate rotation of the bolt and the nut in a loosening direction and to prevent loosening up of the bolt and the nut. The washers are attached to the nut or the bolt in such a manner that the same can slide and rotate but do not come off.