To allow easy assembly of a rolling bearing including a split cage having a plurality of cage segments annularly arranged.

A tool 10 for a split cage 5 having a plurality of cage segments 6 in each of which a plurality of pockets 24 are formed to store tapered rollers 4 and which are annularly arranged along the peripheral direction, includes a restricting part 31 for abutting on the outer peripheral faces of the cage segments 6 in the state that the plurality of cage segments 6 are annularly arranged along the outer periphery of an inner ring 3, to restrict the movement of the cage segments 6 to the radial outside, and a mounting part 32 for fixing the restricting part 31 to the inner ring 3.