<p>A reaction vessel (30) comprises a cup-shaped main container body (302); a through-hole (304) formed on the bottom of the main container body (302); a film formation inhibitor (306) that inhibits blood stored inside the main container body (302) from forming a film on the inner surface of the main container body (302), said inhibitor being formed on at least one part of the inner surface of the main container body (302) between the through-hole (304) and the opening of the main container body (302); and a wet part (308). When blood previously put in the reaction vessel (30) is in contact with the wet part (308), a film of blood initially forms, and when the part of the edge of the blood film that touches the inner surface of the reaction vessel (30) reaches a first super-water-repellent part (306a) or a hydrophobic groove (306c), the film breaks from this area. This reduces the likelihood of a situation in which mixing is prevented due to air getting in between previously stored blood and a newly introduced blood dilution fluid.</p>
