An impeller comprising: a disk section configured to be fixed to a rotary shaft, which rotates about an axis, at least at a first end side in a direction of the axis and configured to extend outward in a radial direction from a second end side opposite to the first end side in the direction of the axis; blade sections provided to protrude from the disk section to the first end side in the direction of the axis; and a cover section integrally provided for the blade sections and configured to cover the blade sections from the first end side in the direction of the axis; wherein the disk section includes a first member and a second member that are divided from each other in the direction of the axis by a dividing plane, which is orthogonal to the axis, at inner sides of the blade sections in the radial direction; and wherein the first member and the second member are joined on the dividing plane; and wherein the first member is capable of being joined to the rotary shaft by shrink-fitting only at a grip section which is provided at the side of a first end thereof, wherein the dividing plane has a step section which has a concave groove which is formed at the first member and has a convex portion which is formed at the second member and is capable of being fitted into the concave groove, wherein the first member and the second member are joined by brazing only on a surface extending in a radial direction of the dividing plane, wherein the concave groove has a backing face which faces the inner side in the radial direction, wherein the convex portion has a mating face which faces the outside in the radial direction, wherein the backing face is connected to a side of an end face of a through-hole of the first member into which the rotary shaft is configured to be inserted, so as to be formed in the dividing plane in the radial direction, and wherein the mating face is connected to a base-section-side region of a front side surface which is a side of an end face of a through-hole of the second member into which the rotary shaft is configured to be inserted, so as to be formed in the dividing plane in the radial direction. a disk section configured to be fixed to a rotary shaft, which rotates about an axis, at least at a first end side in a direction of the axis and configured to extend outward in a radial direction from a second end side opposite to the first end side in the direction of the axis; blade sections provided to protrude from the disk section to the first end side in the direction of the axis; and a cover section integrally provided for the blade sections and configured to cover the blade sections from the first end side in the direction of the axis; wherein the disk section includes a first member and a second member that are divided from each other in the direction of the axis by a dividing plane, which is orthogonal to the axis, at inner sides of the blade sections in the radial direction; and wherein the first member and the second member are joined on the dividing plane; and wherein the first member is capable of being joined to the rotary shaft by shrink-fitting only at a grip section which is provided at the side of a first end thereof, wherein the dividing plane has a step section which has a concave groove which is formed at the first member and has a convex portion which is formed at the second member and is capable of being fitted into the concave groove, wherein the first member and the second member are joined by brazing only on a surface extending in a radial direction of the dividing plane, wherein the concave groove has a backing face which faces the inner side in the radial direction, wherein the convex portion has a mating face which faces the outside in the radial direction, wherein the backing face is connected to a side of an end face of a through-hole of the first member into which the rotary shaft is configured to be inserted, so as to be formed in the dividing plane in the radial direction, and wherein the mating face is connected to a base-section-side region of a front side surface which is a side of an end face of a through-hole of the second member into which the rotary shaft is configured to be inserted, so as to be formed in the dividing plane in the radial direction.