An electrochemical sensor (10) includes a base plate (11) provided with a concave part (12) formed on one of surfaces thereof, a fluid channel (13) formed so that a bottom part (12a) of the concave part (12) and the other one of the surfaces of the base plate (11) are communicated with each other, a plurality of electrodes (16 and 17) formed on the concave part a reagent (19) fixed on the electrodes, a cover (18) which covers the concave part, and an air channel (18a) which causes the inside and outside of the concave part to be communicated with each other.
