Patent ID: 8128795

Claim:
A biosensor being provided with a suction cavity which sucks a certain amount of sample by means of capillary phenomenon, said biosensor comprising: a flow channel to connect said suction cavity and an analytical cavity furnished with a reagent, and a wall portion formed by projecting at least any one of an upper surface, a lower surface, and side walls of said flow channel, said wall portion provided on a part of said flow channel to form a narrowed section, said narrowed section is provided with a gap formed by narrowing a flow passage area due to said wall portion provided on said part of the flow channel, said sample is held back by the wall portion of said narrowed section so that said sample is retained in said suction cavity when the sample is sucked into said suction cavity, and allows the sample accumulated in said suction cavity to circulate into said analytical cavity through said gap, when a centrifugal force is applied from the outside, and said analytical cavity is not provided with an air vent, said analytical cavity vents air displaced by the sample from said suction cavity by way of the gap in the flow channel which communicates with an outlet for venting air provided in said suction cavity, wherein said narrowed section comprises: a first portion where a flow channel area is gradually decreased on the suction cavity side, and a second portion where the flow channel area stays narrow for a predetermined distance between said suction cavity side and said flow channel side, and wherein, said narrow area increases in the rear of said second portion, from said flow channel area having been narrowed to an original area of said flow channel.