A blood sensor to be used in a blood test apparatus, more specifically speaking, a blood sensor which can be easily attached to a blood test apparatus and detached therefrom. Namely, a blood sensor to be detachably attached to a blood test apparatus having a plural number of connectors, which comprises: a supply channel to which blood is supplied; a detection section provided in the supply channel; an electrode system formed in an area including the detection section; a plural number of connection terminals electrically connected to each electrode of the electrode system respectively; and a standard electrode serving as a standard for differentiating these connection terminals. The connectors are connected respectively to the connection terminals and the standard electrode of the blood sensor having been attached to a definite position of the blood test apparatus.