A problem of a sample analysis device that uses magnetic particles is the difficulty in uniformly capturing magnetic particles, specifically the poor uniformity in the vicinity of channel side walls. This causes poor analysis accuracy and reproducibility. The present invention is intended to provide a means to uniformly capture magnetic particles in the vicinity of channel side walls. Specifically, the present invention provides an analysis device that includes a detection channel and a detector. The detection channel has an inlet and an outlet through which a sample liquid containing a specific substance and magnetic particles is flowed in and out of the channel, and magnetic field generating means capable of varying the magnitude of the magnetic field in a predetermined region of the detection channel. The width of the magnet in the detector is greater than the channel width. The detector can improve the analysis accuracy and reproducibility of the analysis device.
