Abstract: A blood test device includes a first substrate with the first opening where the blood is added; a second substrate arranged opposite the first substrate, with a second opening to observe the color reaction; the dry reagent phase laminated on the second surface between the first substrate and the second substrate so that a part of the dry reagent phase is exposed from the second opening; a plasma separation part formed by a porous sheet material and laminated on the dry reagent phase; and a diffusion layer formed by a sheet of hydrophilic fibers and arranged on the plasma separation part so that a part of the diffusion layer is exposed from the first opening, wherein an area of a surface of the plasma separation part on dry reagent phase side, the area being outside a section in contact with the dry reagent phase, is bonded to the second substrate.