Biosensor

A biosensor comprising:

• An insulating base plate;
• an electrode system having a working electrode and a counter electrode which are provided on said base plate;
• a reagent including at least oxidoreductase and an electron mediator;
• a sample solution supply pathway which includes said electrode system and said reagent and has an air aperture on the termination side thereof;
• a sample supply part;
• and a filter which is disposed between said sample solution supply pathway and said sample supply part and filters hemocytes, where plasma with hemocytes therein filtered with said filter is sucked into said sample solution supply pathway due to capillarity,
• characterized by further comprising:
• a first pressing part for holding a primary side portion of said filter from the bottom;
• a second pressing port for holding a secondary side portion of said filter from the top and the bottom;
• a third pressing part for holding the central portion of said filter from the top;
• and a void for surrounding said filter between said second pressing part and third pressing part.