To provide a double washer for a fastening nut of an anchor bolt capable of reliably exercising the function of a washer regardless of the position of the anchor bolt, preventing enlargement of a base plate, and fixing a base of an exposed pedestal of which the position can be easily corrected, by forming leg portions on each washer of the double washer.

This double washer is composed of upper and lower washers formed into the T-shape by forming the leg portions concentrically to seal portions, a bolt hole of a diameter corresponding to a diameter of the anchor bolt 3 is eccentrically formed on the upper washer 2 in a state of being kept into contact with an outer periphery of the leg portion, a diameter of the leg portion of the lower washer 1 is corresponded to an anchor bolt insertion hole 6 formed on the base plate 5, a hole of a diameter corresponding to the diameter of the leg portion of the upper washer is eccentrically formed on the lower washer in a state of being kept into contact with an outer periphery of the leg portion of the lower washer, and the leg portion of the upper washer is inserted into the hole of the lower washer so that the washers are vertically stacked.