Indexable ball end mill

An indexable ball end mill comprising first to third inserts having arcuate cutting edges detachably attached with first to third screws to first to third seats in a semispherical tip end portion of a tool body; a first threaded hole for the first screw slantingly penetrating a slit-shaped first seat; the first insert having an inclined hole to avoid interference between the first screw and the second and third screws; a hole of the first insert and the first screw having at least partially finished surfaces, so that when the first screw penetrates the first insert attached to the first seat, the first insert is precisely positioned by tight engagement of both finished surfaces.