A medium separation device of an automated teller machine, which separates stacked media sheet by sheet and feeds them toward a transfer path, the medium separation device comprising: a pickup roller disposed above the stacked media, the pickup roller having a first friction member provided to protrude from a portion of the outer periphery of a roller body so as to be contacted with the stacked media, the pickup roller sequentially picking up and feeding the stacked media by the first friction member according to the rotation of the roller body; a feed roller disposed to be spaced apart from the pickup roller in a medium feeding direction, the feed roller having a second friction member provided on a portion of the outer periphery of a roller body so as to be contacted with the fed media (11, 12), the feed roller feeding the picked-up and fed media (11, 12) toward a transfer path through the second friction member while rotating with the same phase with the pickup roller; and a medium separation unit disposed below the feed roller, characterized in that the medium separation unit has a plurality of separation rollers (131,132) and a separation belt wound around the separation rollers (131, 132), the medium separation unit separating a following medium, which is simultaneously fed while being in close contact with a preceding medium fed by the pickup roller and the feed roller, from the preceding medium through the friction of the separation belt, the pickup roller being configured to include three pickup rollers arranged to be spaced apart from one another on the same shaft along a direction perpendicular to the medium feeding direction, and in that the feed roller is configured to include two feed rollers disposed to be spaced apart from the pickup rollers in the medium feeding direction, the respective two feed rollers being arranged on the shaft between the three pickup rollers, the medium separation unit being configured to include four medium separation units, and each pair of the medium separation units are disposed below both sides of each feed roller. a pickup roller disposed above the stacked media, the pickup roller having a first friction member provided to protrude from a portion of the outer periphery of a roller body so as to be contacted with the stacked media, the pickup roller sequentially picking up and feeding the stacked media by the first friction member according to the rotation of the roller body; a feed roller disposed to be spaced apart from the pickup roller in a medium feeding direction, the feed roller having a second friction member provided on a portion of the outer periphery of a roller body so as to be contacted with the fed media (11, 12), the feed roller feeding the picked-up and fed media (11, 12) toward a transfer path through the second friction member while rotating with the same phase with the pickup roller; and a medium separation unit disposed below the feed roller, characterized in that the medium separation unit has a plurality of separation rollers (131,132) and a separation belt wound around the separation rollers (131, 132), the medium separation unit separating a following medium, which is simultaneously fed while being in close contact with a preceding medium fed by the pickup roller and the feed roller, from the preceding medium through the friction of the separation belt, the pickup roller being configured to include three pickup rollers arranged to be spaced apart from one another on the same shaft along a direction perpendicular to the medium feeding direction, and in that the feed roller is configured to include two feed rollers disposed to be spaced apart from the pickup rollers in the medium feeding direction, the respective two feed rollers being arranged on the shaft between the three pickup rollers, the medium separation unit being configured to include four medium separation units, and each pair of the medium separation units are disposed below both sides of each feed roller.