A desulfurizing and denitrating apparatus wherein an inner space of a tower body, which has an introduction port for a gas to be processed and a processed gas discharge port formed respectively in opposite side walls, is partitioned in a direction from the side wall having the processed gas introduction port toward the side wall having the processed gas discharge port by an inlet louver, a perforated plate and an outlet louver all extending vertically parallel to each other, a constant-rate discharging device for setting a moving speed of a carbon-base adsorbent in a small chamber defined between the inlet louver and the perforated plate and a constant-rate discharging device for setting a moving speed of a carbon-base adsorbent in a large chamber defined between the perforated plate and the outlet louver are provided, the moving speed of the carbon-base adsorbent in the small chamber is set to be 2 to 4 times greater than an average moving speed, and the distance from the inlet louver to the perforated plate is set to be 0.1 to 0.2 time the distance from the inlet louver to the outlet louver. The carbon-base adsorbent can be prevented from being loaded with dust in the vicinity of the inlet louver, the SO.sub.2 content can be sufficiently lowered in the small chamber, and hence the denitration rate in the large chamber can be increased.