A sensor is disclosed. The sensor includes: an elongated and hollow housing having a first opening formed in a longitudinal direction of the housing, and a second opening formed at one end thereof; a cap closing the second opening; an elongated cover covering the first opening and having one end coupled to the cap; a first receiving groove formed on the housing at a position adjacent to the first opening and facing the cover; a second receiving groove formed on the cap at a position facing the cover; a front sealing member inserted into the first receiving groove and the second receiving groove, and coming into contact with the cover; a groove formed on the cap at a position adjacent to the second opening and facing one end of the housing; and a side sealing member inserted into the groove and coming into contact with the one end of the housing.