PURPOSE: To provide a washer calking tool capable of eaily bending the bending piece of a washer for preventing loosening of a bolt.

CONSTITUTION: A bolt abutting part 15 to be abutted on the head part 41 side surface of a bolt 4 is provided on a head 14 provided on one end of a tool main body 11. A calking member 19 supported on the head 14 via a link 21 is connected to a lever 17 pivotally supported on the head 14 by a pin 20. By abutting the bolt abutting part 15 on the head part 41 of the bolt 4 inserted into a wire connecting link 2 sandwitching a loosening stop washer 5 and operating the lever 17 in the direction of an arrow (b), the calking member 19 is rocked in the direction of an arrow (c), the bending piece 53 of the washer 5 is bent and loosening of the bolt 4 is prevented.