An indexable ball end mill comprising a first insert having arcuate cutting edges (17a, 17b) detachably attached with a first screw to a first seat in a semispherical tip end portion of a tool body, said first seat being constituted by a slit extending in a diametrical direction with a rotation center axis of said semispherical tip end portion as a center, a chip pocket (10, 11) being located in front of said slit in a rotation direction, and said slit dividing said semispherical tip end portion to two half bodies; a first threaded hole for said first screw slantingly penetrating said slit from one half body to the other half body in said semispherical tip end portion; characterized in that: the indexable ball end mill further comprises second and third inserts (13, 14) having arcuate cutting edges (20, 21) detachably attached with second and third screws (15, 16) to second and third seats (5, 6) in a semispherical tip end portion of a tool body; each of said second and third seats (5, 6) being a notch formed in each half body (3a, 3b), each notch comprising a seating surface (5a, 6a) provided in a front surface of each half body (3a, 3b) in a rotation direction, and a chip pocket (5b, 6b) located in front of said seating surface (5a, 6a) in a rotation direction; second and third threaded holes (5c, 6c) for said second and third screws (15, 16) being open on the seating surfaces (5a, 6a) of said second and third seats (5, 6), thereby avoiding interference between said first screw and said second and third screws (15, 16); said first insert having an inclined hole which is aligned with said first threaded hole when said first insert is attached to said first seat; and at least part of the hole of said first insert having a finished surface, said first screw having a finished surface at least partially between its head and its threaded portion, and the finished surface of the hole of said first insert tightly engaging the finished surface of said first screw when said first screw penetrates said first insert attached to said first seat, thereby precisely positioning said first insert. the indexable ball end mill further comprises second and third inserts (13, 14) having arcuate cutting edges (20, 21) detachably attached with second and third screws (15, 16) to second and third seats (5, 6) in a semispherical tip end portion of a tool body; each of said second and third seats (5, 6) being a notch formed in each half body (3a, 3b), each notch comprising a seating surface (5a, 6a) provided in a front surface of each half body (3a, 3b) in a rotation direction, and a chip pocket (5b, 6b) located in front of said seating surface (5a, 6a) in a rotation direction; second and third threaded holes (5c, 6c) for said second and third screws (15, 16) being open on the seating surfaces (5a, 6a) of said second and third seats (5, 6), thereby avoiding interference between said first screw and said second and third screws (15, 16); said first insert having an inclined hole which is aligned with said first threaded hole when said first insert is attached to said first seat; and at least part of the hole of said first insert having a finished surface, said first screw having a finished surface at least partially between its head and its threaded portion, and the finished surface of the hole of said first insert tightly engaging the finished surface of said first screw when said first screw penetrates said first insert attached to said first seat, thereby precisely positioning said first insert.