The present invention relates to a microchip 1 having a translucent member 11, a flow channel 10 or a cell formed at a side of the translucent member 11 where light enters, and an aperture 16 formed at a position corresponding to the flow channel 10 or the cell at a side of a translucent member 10 where light goes out. The aperture 16 has a light go-through surface 17 which causes light flux being emitted from the flow channel 10 or the cell to go through and a light reflective surface 18 that totally reflects the incident light flux. A width size W1 of the light go-through surface 17 is smaller than a width size W2 of the flow channel 10 or the cell.