An excellent photosensitivity is exhibited by a protein including, at a position or positions corresponding to one or two or more positions selected from the group made of the following (1) to (3) in a first amino acid sequence represented by SEQ ID NO: 1: (1) positions 39, 94, 98, 102, 110, 113, 114, 162, 224, 225, 230, 231, and 235, (2) positions 53, 61, 68, 74, 76, 80, 130, 137, 194, 195, 198, 200, 204, 205, 209, 210, 253, and 254, and (3) positions 46, 83, 84, 87, 90, 91, 116, 117, 120, 124, 139, 142, 143, 146, 173, 214, 216, 217, 238, 242, and 245, an amino acid residue different from that in the first amino acid sequence, and that has channel activity.