To improve reaction efficiency by increasing a contact area of first and second reactants per unit volume, without reducing dimensions of the inlet paths for the first and second reactants in a layer-thickness direction, a channel includes a first inlet path having the first reactant, a parallel second inlet path separated from the first inlet path and having the second reactant, a junction channel for causing the first and second reactants to join as separate laminar flows, and a parallel reaction channel connected with a downstream side of the junction channel for permitting the laminar flows of the first and second reactants to react at a contact interface thereof. A dimension of the reaction channel in the layer-thickness direction perpendicular to the contact interface is set to be smaller than the sum of the dimensions of the first inlet path and the second inlet path in the layer-thickness direction.