A double-sided cutting insert includes: rectangular shaped upper and lower surfaces formed at upper and lower sides of the insert; four side surfaces of each of the upper and lower surfaces; an assembling hole perpendicular to the upper surface; major cutting edges, at corners of one side surface, and rotationally symmetrical with respect to a center of an outer shape of the insert in a plan view where the upper surface is the front and rotationally symmetrical with respect to the center in a front view where the one of the side surfaces is the front; minor cutting edges, formed at one side of each major cutting edge, and rotationally symmetrical with respect to the center in the plan view; and minor side surfaces formed on a surface where the minor cutting edges meet the side surfaces and inclined toward the center with respect to an assembling hole central axis.