A plurality of fluid feed pipes having fluid percolation walls are arranged in a container, through which solid particles move downward, and the fluid passes through the pipes so that the contacts between the solid particles and the fluid are made with a low pressure loss. A plurality of solid particle feed pipes for forming spaces enclosed by fluid percolation walls are arranged in a container, through which the fluid flows, and the solid particles move through the solid particle feed pipes so that the contacts between the solid particles and the fluid are made with a low pressure loss. A plurality of bottom-opened fluid passages and having polygonal or semicircular sections are disposed in a container, through which solid particles move downward, and the fluid passes through the fluid passages so that the contacts between the solid particles and the fluid are made with a low pressure loss.