To provide an analyzer which can perform quantitative measurement of a sample containing a substance to be analysed without the need of dilution of the sample.

A pre-processing part in which a substance reducing the molar amount is fixed is provided upstream of a detecting part provided in a fine flow channel in flow direction. A substance to be detected is captured by a capture body of the pre-processing part and therefore reduced, thereby making it possible to keep the concentration of the substance to be detected on the detecting part within the calibration range of the detecting part.