A turbine casing, comprising: a shroud of a cylindrical shape defining an operational flow path between the shroud and a hub of a turbine rotor; a scroll outer peripheral wall continuing from an end side of the shroud and extending along a circumferential direction of the shroud; and a partition wall disposed inside the scroll outer peripheral wall and dividing an inside of the scroll outer peripheral wall into a first scroll flow path and a second scroll flow path disposed adjacent to each other in an axial direction of the shroud, wherein the shroud, the scroll outer peripheral wall, and the partition wall are formed integrally by casting, wherein the partition wall, from a root end to a far end, is formed of molten metal poured into a runner formed between a main mold and a core, wherein the partition wall has a widening section which partially increases a communication area between at least two of the first scroll flow path, the second scroll flow path, and the operational flow path, in the circumferential direction of the shroud, wherein the widening section includes at least one cutout portion provided for an inner peripheral side of the partition wall, wherein the scroll outer peripheral wall includes a tongue section at a most downstream position of the first scroll flow path and the second scroll flow path in a flow direction of a fluid, wherein the at least one cutout portion includes a downstream cutout portion (61, 62) extending downstream in the flow direction of the fluid from a position of at least 90 and no more than 270 degrees in the circumferential direction of the shroud, where a position in the circumferential direction of the shroud is represented with reference to a position of the tongue section as a zero-degree position and the flow direction of the fluid as a positive direction, characterized in that the scroll outer peripheral wall has such a shape that A/R of a flow path combining the first scroll flow path and the second scroll flow path in a region where the downstream cutout portion (61, 62) is formed is smaller than an A/R distribution in a case where a total of A/R of the first scroll flow path and the second scroll flow path at an upstream side of the downstream cutout portion (61, 62) linearly decreases toward 360 degrees. a scroll outer peripheral wall continuing from an end side of the shroud and extending along a circumferential direction of the shroud; and a partition wall disposed inside the scroll outer peripheral wall and dividing an inside of the scroll outer peripheral wall into a first scroll flow path and a second scroll flow path disposed adjacent to each other in an axial direction of the shroud, wherein the shroud, the scroll outer peripheral wall, and the partition wall are formed integrally by casting, wherein the partition wall, from a root end to a far end, is formed of molten metal poured into a runner formed between a main mold and a core, wherein the partition wall has a widening section which partially increases a communication area between at least two of the first scroll flow path, the second scroll flow path, and the operational flow path, in the circumferential direction of the shroud, wherein the widening section includes at least one cutout portion provided for an inner peripheral side of the partition wall, wherein the scroll outer peripheral wall includes a tongue section at a most downstream position of the first scroll flow path and the second scroll flow path in a flow direction of a fluid, wherein the at least one cutout portion includes a downstream cutout portion (61, 62) extending downstream in the flow direction of the fluid from a position of at least 90 and no more than 270 degrees in the circumferential direction of the shroud, where a position in the circumferential direction of the shroud is represented with reference to a position of the tongue section as a zero-degree position and the flow direction of the fluid as a positive direction, characterized in that the scroll outer peripheral wall has such a shape that A/R of a flow path combining the first scroll flow path and the second scroll flow path in a region where the downstream cutout portion (61, 62) is formed is smaller than an A/R distribution in a case where a total of A/R of the first scroll flow path and the second scroll flow path at an upstream side of the downstream cutout portion (61, 62) linearly decreases toward 360 degrees.