To provide a locking washer capable of being fastened in a small number of processes and successfully achieving a high locking effect and a locking fastener using the same.

The locking washer 1, which is fastened with a locking nut 2 formed with a tapered circular inclined depression 22 on the seating surface side, includes a washer hole 11 in which a threaded shaft 4 is inserted, a circular arc-shaped inclined projection 12 formed along the washer hole 11 in a circular arc-shape and in a projected and tapered shape an outer circumferential surface diameter reduced in the projecting direction, and a thread groove engagement portion 13 formed along the inner circumference of the circular arc-shaped inclined projection 12 to be engaged with the thread groove of the threaded shaft 4.