A microchip formed by two substrate layers (a, b) laminated onto each other and on which a fluid channel structure is formed, the fluid channel structure comprising: - a first introduction channel; - two second introduction channels (21, 22) arranged to sandwich the first introduction channel and merged with the first introduction channel from both sides; and - a merge channel connected to the first introduction channel and the second introduction channels (21, 22), where fluids fed from the first and the second introduction channels are merged and flow, wherein the merge channel has a tapered portion to suppress spiral flow field generated after the merging and formed so that a channel depth in a direction perpendicular to a plane containing the first introduction channel and the second introduction channels (21, 22) gradually decreases along a fluid feeding direction and a channel width in a sandwiching direction along which the first introduction channel is sandwiched by the second introduction channels (21, 22) gradually increases along a fluid feeding direction, and a contracted portion disposed downstream of the tapered portion and formed so that that the channel depth and the channel width gradually decrease along the fluid feeding direction, the tapered portion and the contracted portion are formed discontinuously, wherein a part of the second introduction channels (21, 22) and a part of the merge channel are made on a first substrate layer (a), wherein the first introduction channel, a part of the second introduction channels (21, 22) and a part of the merge channel are made on a second substrate layer (b), wherein the merge channel downstream of the tapered portion and the contracted portion is made on the second substrate layer (b), and wherein the merge channel upstream of the contracted portion, including the tapered portion, and the contracted portion are fabricated on the two substrate layers (a, b). - a first introduction channel; - two second introduction channels (21, 22) arranged to sandwich the first introduction channel and merged with the first introduction channel from both sides; and - a merge channel connected to the first introduction channel and the second introduction channels (21, 22), where fluids fed from the first and the second introduction channels are merged and flow, wherein the merge channel has a tapered portion to suppress spiral flow field generated after the merging and formed so that a channel depth in a direction perpendicular to a plane containing the first introduction channel and the second introduction channels (21, 22) gradually decreases along a fluid feeding direction and a channel width in a sandwiching direction along which the first introduction channel is sandwiched by the second introduction channels (21, 22) gradually increases along a fluid feeding direction, and a contracted portion disposed downstream of the tapered portion and formed so that that the channel depth and the channel width gradually decrease along the fluid feeding direction, the tapered portion and the contracted portion are formed discontinuously, wherein a part of the second introduction channels (21, 22) and a part of the merge channel are made on a first substrate layer (a), wherein the first introduction channel, a part of the second introduction channels (21, 22) and a part of the merge channel are made on a second substrate layer (b), wherein the merge channel downstream of the tapered portion and the contracted portion is made on the second substrate layer (b), and wherein the merge channel upstream of the contracted portion, including the tapered portion, and the contracted portion are fabricated on the two substrate layers (a, b). wherein the merge channel has a tapered portion to suppress spiral flow field generated after the merging and formed so that a channel depth in a direction perpendicular to a plane containing the first introduction channel and the second introduction channels (21, 22) gradually decreases along a fluid feeding direction and a channel width in a sandwiching direction along which the first introduction channel is sandwiched by the second introduction channels (21, 22) gradually increases along a fluid feeding direction, and a contracted portion disposed downstream of the tapered portion and formed so that that the channel depth and the channel width gradually decrease along the fluid feeding direction, the tapered portion and the contracted portion are formed discontinuously, wherein a part of the second introduction channels (21, 22) and a part of the merge channel are made on a first substrate layer (a), wherein the first introduction channel, a part of the second introduction channels (21, 22) and a part of the merge channel are made on a second substrate layer (b), wherein the merge channel downstream of the tapered portion and the contracted portion is made on the second substrate layer (b), and wherein the merge channel upstream of the contracted portion, including the tapered portion, and the contracted portion are fabricated on the two substrate layers (a, b).