A microchip comprising: an inlet which is open at the distal end of a protruding section which protrudes from one side face of the microchip body; wherein in use the microchip is attached to a microchip holding member, so that rotary drive means provided in an analyzer are operable to rotate the microchip holding member and the microchip in a predetermined direction about an axis; wherein the inlet protrudes beyond one side surface of the microchip body toward the axis; wherein in the periphery of the inlet, the one side surface of the microchip has formed thereon a concave portion which is open only to the axis side; and is depressed in the outer peripheral direction from the axis, wherein the concave portion is gently curved in such a manner that, in the opening of the concave portion, the cross-sectional area on the axis side is equal to or greater than that on the outer peripheral side; a first capillary cavity (4, 17) for collecting a specific amount of a liquid sample by capillary force, one end of the first capillary cavity (4, 17) being connected to the inlet and a first holding chamber for receiving the liquid sample transferred from the first capillary cavity (4, 17) by centrifugal force generated by rotation about the axis, the holding chamber connected to the other end of the first capillary cavity (4, 17); a cavity (15, 16) connecting the inlet with the first holding chamber, wherein the cavity (15, 16) is provided to one side face of the first capillary cavity (4, 17), the cavity (15, 16) communicating with the atmosphere without generating capillary force; wherein an arrangement of the capillary cavity (4, 17) and the cavity (15, 16) is one of the following: i) cross-sectional shapes of the first capillary cavity (4, 17) and the cavity (15, 16) are rectangular; the cavity (15, 16) is greater in cross-sectional size in a thickness direction than the first capillary cavity (4, 17); and the cavity (15, 16) is formed to one side or opposite sides of the first capillary cavity (4, 17); or ii) a portion of a cross section of the first capillary cavity (4, 17) is arc-shaped; a cross section of the cavity (15, 16) is rectangular; the cavity (15, 16) is greater in cross-sectional size in a thickness direction than the first capillary cavity (4, 17); and the cavity (15, 16) is formed to one side or opposite sides of the first capillary cavity (4, 17); or iii) portions of cross sections of the first capillary cavity (4, 17) and the cavity are arc-shaped; and the cavity (15, 16) is formed to one side or opposite sides of the first capillary cavity (4, 17); or iv) a wall of the cavity (15, 16) is a hydrophobic surface. an inlet which is open at the distal end of a protruding section which protrudes from one side face of the microchip body; wherein in use the microchip is attached to a microchip holding member, so that rotary drive means provided in an analyzer are operable to rotate the microchip holding member and the microchip in a predetermined direction about an axis; wherein the inlet protrudes beyond one side surface of the microchip body toward the axis; wherein in the periphery of the inlet, the one side surface of the microchip has formed thereon a concave portion which is open only to the axis side; and is depressed in the outer peripheral direction from the axis, wherein the concave portion is gently curved in such a manner that, in the opening of the concave portion, the cross-sectional area on the axis side is equal to or greater than that on the outer peripheral side; a first capillary cavity (4, 17) for collecting a specific amount of a liquid sample by capillary force, one end of the first capillary cavity (4, 17) being connected to the inlet and a first holding chamber for receiving the liquid sample transferred from the first capillary cavity (4, 17) by centrifugal force generated by rotation about the axis, the holding chamber connected to the other end of the first capillary cavity (4, 17); i) cross-sectional shapes of the first capillary cavity (4, 17) and the cavity (15, 16) are rectangular; the cavity (15, 16) is greater in cross-sectional size in a thickness direction than the first capillary cavity (4, 17); and the cavity (15, 16) is formed to one side or opposite sides of the first capillary cavity (4, 17); or ii) a portion of a cross section of the first capillary cavity (4, 17) is arc-shaped; a cross section of the cavity (15, 16) is rectangular; the cavity (15, 16) is greater in cross-sectional size in a thickness direction than the first capillary cavity (4, 17); and the cavity (15, 16) is formed to one side or opposite sides of the first capillary cavity (4, 17); or iii) portions of cross sections of the first capillary cavity (4, 17) and the cavity are arc-shaped; and the cavity (15, 16) is formed to one side or opposite sides of the first capillary cavity (4, 17); or iv) a wall of the cavity (15, 16) is a hydrophobic surface.