A reagent-containing assembly comprising: a reagent container (210, 220, 310) comprising an opening (212a, 222a, 312a) sealed by a seal member (210a, 220a, 310a); a reagent container holder (230, 320) configured for detachably holding the reagent container (210, 220, 310); a case main body (250, 340) for covering the side surface of the reagent container (210, 220, 310); and a seal-opening section (260, 350) comprising a breaking portion (271c, 272c, 361c) for breaking the seal member (210a, 220a, 310a), and a suction hole configured to provide access to the reagent container (210, 220, 310); characterized in that: the reagent container holder (230, 320) and the case main body (250, 340) are configured for detachable engagement with each other, wherein the seal-opening section (260, 350) comprises a lid part (280, 290, 370) configured to open and close the suction hole, in that: the seal-opening section (260, 350) is fixedly attached to the case main body (250, 340) that is formed into a box shape having one end opened for accommodating the reagent container (210, 220, 310); in that the reagent container holder (230, 320) comprises a closing part (235, 324) for closing the open end of the case main body (250, 340); and in that: the case main body (250, 340) and the reagent container holder (230, 320) are configured so that the open end is closed by the closing part (235, 324) after the seal member (210a, 220a, 310a) is broken by the breaking portion (271c, 272c, 361c). a reagent container (210, 220, 310) comprising an opening (212a, 222a, 312a) sealed by a seal member (210a, 220a, 310a); a reagent container holder (230, 320) configured for detachably holding the reagent container (210, 220, 310); a case main body (250, 340) for covering the side surface of the reagent container (210, 220, 310); and a seal-opening section (260, 350) comprising a breaking portion (271c, 272c, 361c) for breaking the seal member (210a, 220a, 310a), and a suction hole configured to provide access to the reagent container (210, 220, 310); the reagent container holder (230, 320) and the case main body (250, 340) are configured for detachable engagement with each other, wherein the seal-opening section (260, 350) comprises a lid part (280, 290, 370) configured to open and close the suction hole, in that: the seal-opening section (260, 350) is fixedly attached to the case main body (250, 340) that is formed into a box shape having one end opened for accommodating the reagent container (210, 220, 310); in that the reagent container holder (230, 320) comprises a closing part (235, 324) for closing the open end of the case main body (250, 340); and in that: the case main body (250, 340) and the reagent container holder (230, 320) are configured so that the open end is closed by the closing part (235, 324) after the seal member (210a, 220a, 310a) is broken by the breaking portion (271c, 272c, 361c). the seal-opening section (260, 350) is fixedly attached to the case main body (250, 340) that is formed into a box shape having one end opened for accommodating the reagent container (210, 220, 310); in that the reagent container holder (230, 320) comprises a closing part (235, 324) for closing the open end of the case main body (250, 340); and in that: the case main body (250, 340) and the reagent container holder (230, 320) are configured so that the open end is closed by the closing part (235, 324) after the seal member (210a, 220a, 310a) is broken by the breaking portion (271c, 272c, 361c). the case main body (250, 340) and the reagent container holder (230, 320) are configured so that the open end is closed by the closing part (235, 324) after the seal member (210a, 220a, 310a) is broken by the breaking portion (271c, 272c, 361c).