PROBLEM TO BE SOLVED: To provide a commutation device arranged in a conduit for transferring and isolating a fluid laminar flow while commutating a fluid core part to a conduit outer circumference and commutating an outer circumferential flow to a center of the conduit. SOLUTION: The commutation device includes a disk arranged in a lateral direction of a conduit length, having an outer side outer shape for sealing and engaging by a shape following an inner side outer shape of the conduit. An array of slots extends in a periphery of the disk, and the fluid core part is faced to the inner side outer shape of the conduit, and the outer circumferential flow is faced to the fluid core part simultaneously. The slots are alternately arranged, and isolation of the fluid core part and an outer circumferential fluid in commutation is maintained.