A contactor (1a, 1b) in which an upflow fluid being a light liquid is fed from a lower part in a column and a downflow fluid being a heavy liquid being immiscible with the light liquid is fed from an upper part of the column and the light liquid as the upflow fluid and the heavy liquid as the downflow fluid are subjected to countercurrent contacting, comprising: providing a plurality of stages of cells (22, 32) in a manner that the upper stage side cell and the lower stage side cell neighboring each other along flow paths of the upflow fluid and the downflow fluid are on different stages, the cell forming a countercurrent contacting space of the upflow fluid and the downflow fluid; separating the upper stage side cell and the lower stage side cell by a vertical partition wall and horizontal partition walls (21, 31); and providing, as constitution, in the partition wall of the respective stages, downflow fluid injection holes in a lower part of the vertical wall of the upper stage side cell, wherein the downflow fluid injection holes are constituted with (i) a plurality of slits extending in the lateral direction and being arranged in the longitudinal direction or (ii) circular hole sections numerously arranged in the lateral direction and the longitudinal direction, so that the downflow fluid, which resides by being blocked by the partition wall, injects into the lower stage side cell, providing an upflow fluid flow-in port constituted with a slit or slits extending in a horizontal direction immediately below the horizontal partition wall which constitutes a ceiling surface of the lower stage side cell as in a state that a lower surface of the horizontal partition wall and an upper peripheral edge of the upflow fluid flow-in port are common, in an upper side than a region in which the downflow fluid resides, through the upflow fluid flow-in port the upflow fluid from the lower stage side cell flowing into the upper stage side cell, and providing a wall part without holes in a middle area of the partition wall between the lower part of the wall with the downflow fluid injection holes and the upflow fluid flow-in port in the upper side, or providing, as constitution, in the partition wall of the respective stages, upflow fluid injection holes in an upper part of the vertical wall of the lower stage side cell, wherein the upflow fluid injection holes are constituted with (i) a plurality of slits extending in the lateral direction and being arranged in the longitudinal direction or (ii) circular hole sections numerously arranged in the lateral direction and the longitudinal direction, so that the upflow fluid, which resides in the lower stage side cell, injects by its buoyancy into the upper stage side cell, and providing immediately above the horizontal partition wall which constitutes a bottom surface of the upper stage side cell, in a lower side than the upflow fluid injection holes a downflow fluid flow-in port constituted with a slit or slits extending in a horizontal direction through which the downflow fluid from the upper stage side cell flows by its potential energy into the lower stage side cell as in a state that an upper surface of the horizontal partition wall and a lower peripheral edge of the downflow fluid flow-in port are common, and providing a wall part without holes in a middle area of the partition wall between the upper part of the wall with the upflow fluid injection holes and the downflow fluid flow-in port in the lower side. providing a plurality of stages of cells (22, 32) in a manner that the upper stage side cell and the lower stage side cell neighboring each other along flow paths of the upflow fluid and the downflow fluid are on different stages, the cell forming a countercurrent contacting space of the upflow fluid and the downflow fluid; separating the upper stage side cell and the lower stage side cell by a vertical partition wall and horizontal partition walls (21, 31); and providing, as constitution, in the partition wall of the respective stages, downflow fluid injection holes in a lower part of the vertical wall of the upper stage side cell, wherein the downflow fluid injection holes are constituted with (i) a plurality of slits extending in the lateral direction and being arranged in the longitudinal direction or (ii) circular hole sections numerously arranged in the lateral direction and the longitudinal direction, so that the downflow fluid, which resides by being blocked by the partition wall, injects into the lower stage side cell, providing an upflow fluid flow-in port constituted with a slit or slits extending in a horizontal direction immediately below the horizontal partition wall which constitutes a ceiling surface of the lower stage side cell as in a state that a lower surface of the horizontal partition wall and an upper peripheral edge of the upflow fluid flow-in port are common, in an upper side than a region in which the downflow fluid resides, through the upflow fluid flow-in port the upflow fluid from the lower stage side cell flowing into the upper stage side cell, and providing a wall part without holes in a middle area of the partition wall between the lower part of the wall with the downflow fluid injection holes and the upflow fluid flow-in port in the upper side,