A sprinkler of an underground irrigation apparatus is provided to allow irrigation water to be smoothly supplied to an underground area in which crops or other plants are planted, thereby helping the growth of the crops or plants. A sprinkler(10) of an underground irrigation apparatus(23) comprises: a main body(11); an inlet(13) which is formed at the upper part of the main body and connected to a connection hose(21); a pointed part(12) which is formed at the lower part of the main body and has a conic front end; a guide passage(14) which is formed inside the main body and extended from the inlet near the pointed part; and an outlet(15) which is formed near the pointed part and joined to the guide passage and has an opening consisting of a pierced hole and a cover. The cover has a projecting piece that projects to the front of the pierced hole.
