PURPOSE: To provide a step tower which can carry out good gas-liquid contact while preventing the liquid loss to the outside of a tank due to entrainment by putting regular packing materials among a plurality of trays of a counter flow contact-type step tower.

CONSTITUTION: A plurality of trays 21, 22,... are put in a cylindrical tank 1. On the down face of a plurality of the trays 21, 22,... or in the middle of a plurality of the trays 21, 22,..., regular packing materials 31, 32,... are put and fitted. The regular packing materials 31, 32,... are an integrated body prepared by layering Rasching rings, ring bricks regularly. The regular packing materials 31, 32,... form thin films by applying a liquid on their surfaces and improve the gas-liquid contact and moreover the liquid on a tray is foamed on the tray and becomes dewdrops by breaking the foams and the resulting dewdrops are captured by the regular packing materials 31, 32,... and the liquid is prevented from leaking to the outside of the tank due to entrainment.