The present invention relates to a drainage apparatus for a sink, in which it is possible to drain wash water rapidly without having residue substances such as foreign substances and the like caught thereon, and prevent leakage of malodor in advance, thereby achieving excellent cleanliness, facilitating an operation and maintenance of the drainage apparatus due to its simple configuration and structure. Thus, according to the drainage apparatus for a sink of the invention, residue substances, foreign substances and the like are not caught on the drainage apparatus, the female screw-shaped grooves induce vortex of wash water, thereby rapidly draining the wash water, and the float ball made of positive buoyancy material is insertingly mounted inside of the tubular drainage body so as to ascend or descend by means of the wash water, thereby preventing leakage of malodor in advance, achieving excellent cleanliness, and facilitating an assembling operation and maintenance/repair of the drainage apparatus due to its simple configuration and structure.