An analysis device having a microchannel structure that transfers a sample liquid by centrifugal force towards a measurement chamber formed in an analysis device main body having, formed inside, a microchannel structure with minute surface irregularities, the sample liquid being collected into the microchannel structure of the analysis device main body from an inlet formed thereon, and being used for reading involving accessing a reaction liquid by optical measurement at a measurement spot in the measurement chamber, the analysis device comprising: a protective cap pivotally supported on the analysis device main body so as to be rotationally movable between an open position that exposes the inlet and a closed position that covers a part of the analysis device main body and prevents scattering of the sample liquid from the inlet; a diluent container whose opening is sealed by a seal member so as to internally hold a diluent; a diluent container containing section formed inside the analysis device main body and which contains the diluent container such that the diluent container is movable between a liquid holding position and a liquid discharge position; and a protrusion provided on the diluent container containing section and arranged along a movement path of the diluent container from the liquid holding position to the liquid discharge position such that the seal member of the diluent container is broken by the protrusion when the diluent container is moved to the liquid discharge position so as to open the diluent container, characterized in that the diluent container and a part of the protective cap at the closed position before moving to the open position to expose the inlet are in direct or indirect engagement with each other so as to lock the diluent container to the liquid holding position and prevent the diluent container from moving to the liquid discharge position, and the diluent container is moved to the open position where the seal member engages the protrusion to be broken by a shifting of the protective cap from the open position to the closed position. a protective cap pivotally supported on the analysis device main body so as to be rotationally movable between an open position that exposes the inlet and a closed position that covers a part of the analysis device main body and prevents scattering of the sample liquid from the inlet; a diluent container whose opening is sealed by a seal member so as to internally hold a diluent; a diluent container containing section formed inside the analysis device main body and which contains the diluent container such that the diluent container is movable between a liquid holding position and a liquid discharge position; and a protrusion provided on the diluent container containing section and arranged along a movement path of the diluent container from the liquid holding position to the liquid discharge position such that the seal member of the diluent container is broken by the protrusion when the diluent container is moved to the liquid discharge position so as to open the diluent container, characterized in that the diluent container and a part of the protective cap at the closed position before moving to the open position to expose the inlet are in direct or indirect engagement with each other so as to lock the diluent container to the liquid holding position and prevent the diluent container from moving to the liquid discharge position, and the diluent container is moved to the open position where the seal member engages the protrusion to be broken by a shifting of the protective cap from the open position to the closed position.