Square end mill includes long end cutting edge disposed from end portion on outer peripheral side in radial direction to center in the radial direction when a cutting edge portion is viewed from end face side, and short end cutting edges disposed from other end portions on outer peripheral side in radial direction to middles on center side in radial direction, first gashes disposed on regions from lines connecting end portions on center side in radial direction of the short end cutting edges to center in radial direction to the long end cutting edge on rear side in the rotation direction, second and third gashes disposed on rear and front sides in rotation direction of the first gashes, and all gashes formed in curved surface shapes depressed to a shank side on opposite side in axial direction of the cutting edge portion.