Disclosed is an insert for a construction slab which includes: main body in which an operation space having a planar cross-section of a polygonal shape in an axial direction is formed; a support block which is formed at a lower side of the main body to have a diameter smaller than that of the main body and has a withdrawal hole at an inner side thereof so that a support stepped portion is formed at a lower end of the operation space; a support plate formed at the lower side of the support block to be in contact with a mold; a cover member coupled to an upper portion of the main body so as to seal the operation space; and an anchor bolt member inserted into the operation space to be pressed to the withdrawal hole by a spring member.