To make a moving bed volume small by dividing a discharge hopper of a moving bed into two or more, allowing a moving velocity distribution of the particles to correspond to reaction characteristics between the particles and gas or the adsorption characteristics, and controlling a particle discharge quantity so as to make a reaction quantity or an absorption quantity uniform.

This hopper for controlling the particle discharge quantity which is provided on the lower part of a moving bed (hereafter the hopper) is divided into two or more in the gas flow direction, e.g. into hoppers 7, 8 and 9. The moving bed particles 1 are fed from a particle feed part 6 and are discharged from the hoppers 7, 8, 9, then form the moving bed, and are orthogonally crossed with exhaust gas. Respective particle discharge flow quantities Q1, Q2 and Q3 of the hoppers 7, 8 and 9 are controlled by the particle discharge flow quantity so as to impart, e.g. an A characteristics of the moving velocity distribution in accordance with adsorption-time characteristics of the moving bed particles 1. Thus, SOx adsorption quantities of the moving bed particles 1 at respective horizontal cross-sections of the moving bed become uniform and the height of the moving bed can be shortened.