A halved outer ring (11a, 11b, 41, 51, 61) for use in a roller bearing and having a substantially semicylindrical shape, wherein: protruding (17a, 46a, 56a) and recessed (17b, 46b, 56b) shapes are provided in abutting portions (16a, 16b, 16c, 42, 52) where a pair of said halved outer rings (11a, 11b, 41, 51, 61) abut on each other when fitted on a rotary shaft that is supported by said roller bearing, and said protruding (17a, 46a, 56a) and recessed (17b, 46b, 56b) shapes are configured to mesh with each other to restrict axial movement of said halved outer rings (11a, 11b, 41, 51, 61), and said protruding (17a, 46a, 56a) and recessed (17b, 46b, 56b) shapes are point-symmetric with respect to a center of a positioning portion, characterized by the positioning portion provided in a center of an outer diameter surface in both circumferential and axial directions, and configured to engage with a housing, which is placed on an outer diameter side of said halved outer ring (11a, 11b, 41, 51, 61), to position said halved outer ring (11a, 11b, 41, 51, 61) with respect to said housing, wherein when said abutting portion (16a, 16b, 16c, 42, 52) is viewed from said outer diameter side, said protruding shape (17a, 46a, 56a) is formed by a first line extending straight in said circumferential direction, and a second line extending from an outer circumferential end of said first line to one axial end of said halved outer ring (11a, 11b, 41, 51, 61), and said recessed shape (17b, 46b; 56b) is formed by said first line and a third line extending from an inner circumferential end of said first line to the other axial end of said halved outer ring (11a, 11b, 41, 51, 61). protruding (17a, 46a, 56a) and recessed (17b, 46b, 56b) shapes are provided in abutting portions (16a, 16b, 16c, 42, 52) where a pair of said halved outer rings (11a, 11b, 41, 51, 61) abut on each other when fitted on a rotary shaft that is supported by said roller bearing, and said protruding (17a, 46a, 56a) and recessed (17b, 46b, 56b) shapes are configured to mesh with each other to restrict axial movement of said halved outer rings (11a, 11b, 41, 51, 61), and said protruding (17a, 46a, 56a) and recessed (17b, 46b, 56b) shapes are point-symmetric with respect to a center of a positioning portion, characterized by the positioning portion provided in a center of an outer diameter surface in both circumferential and axial directions, and configured to engage with a housing, which is placed on an outer diameter side of said halved outer ring (11a, 11b, 41, 51, 61), to position said halved outer ring (11a, 11b, 41, 51, 61) with respect to said housing, wherein when said abutting portion (16a, 16b, 16c, 42, 52) is viewed from said outer diameter side, said protruding shape (17a, 46a, 56a) is formed by a first line extending straight in said circumferential direction, and a second line extending from an outer circumferential end of said first line to one axial end of said halved outer ring (11a, 11b, 41, 51, 61), and said recessed shape (17b, 46b; 56b) is formed by said first line and a third line extending from an inner circumferential end of said first line to the other axial end of said halved outer ring (11a, 11b, 41, 51, 61).