An anchor is provided to reinforce fixation of an anchor under the ground by splaying an anchor extending body toward the inner wall of an excavation with an extending cap. An anchor comprises an anchor extending body(30) and an extending unit. The anchor extending body includes a case(31) and extendable portions(32). The case covers the external circumference of the anchor main body. The extendable portions are attached to the case circumferentially at regular intervals, and extend from the end of the case. The extending unit includes an extending cap(50). The extending cap is installed under the anchor extending body. The upper end diameter of the extending cap is smaller than the diameter of the anchor extending body, and gets smaller to the lower end.
