A water supply tube for a steam generator comprising: an insert tube portion configured to horizontally extend and to be inserted in a penetration hole penetrating a shell member of the steam generator; and a generator internal tube portion connected to the insert tube portion and configured to be arranged inside the steam generator, wherein the generator internal tube portion includes a tubular passage formed in an axial direction of the generator internal tube portion and an effluence unit allowing effluence of cooling water in the tubular passage from the tubular passage to a space in the steam generator, the tubular passage allowing cooling water supplied from outside the steam generator via the insert tube portion to flow in the tubular passage, wherein the tubular passage includes a first tilted portion which is tilted so that a side having a greater distance from the insert tube portion along a flow direction of cooling water is located vertically higher than a side having a smaller distance from the insert tube portion and a second tilted portion which is located with a greater distance from the insert tube portion along the flow direction than the first tilted portion and is tilted so that a side having a greater distance from the insert tube portion along the flow direction is located vertically lower than a side having a smaller distance from the insert tube portion, and wherein, in at least a portion of a section, along the flow direction, of the tubular passage between the first tilted portion and the second tilted portion, a bottom end of a cross section, perpendicular to the flow direction, of the tubular passage is arranged vertically higher than a horizontal plane including a top end of an inner wall surface of the insert tube portion at a connection between the insert tube portion and the generator internal tube portion, the water supply tube being characterized in that the generator internal tube portion includes a connection tube portion and a tilted tube portion, the connection tube portion being tilted so that an end portion side connected to an upper horizontal tube portion is located vertically higher than an end portion side connected to the insert tube portion, and the tilted tube portion being tilted so that a side with an end portion connected to a horizontal ring tube portion is located vertically lower than a side with an end portion connected to the upper horizontal tube portion. an insert tube portion configured to horizontally extend and to be inserted in a penetration hole penetrating a shell member of the steam generator; and a generator internal tube portion connected to the insert tube portion and configured to be arranged inside the steam generator, wherein the generator internal tube portion includes a tubular passage formed in an axial direction of the generator internal tube portion and an effluence unit allowing effluence of cooling water in the tubular passage from the tubular passage to a space in the steam generator, the tubular passage allowing cooling water supplied from outside the steam generator via the insert tube portion to flow in the tubular passage, wherein the tubular passage includes a first tilted portion which is tilted so that a side having a greater distance from the insert tube portion along a flow direction of cooling water is located vertically higher than a side having a smaller distance from the insert tube portion and a second tilted portion which is located with a greater distance from the insert tube portion along the flow direction than the first tilted portion and is tilted so that a side having a greater distance from the insert tube portion along the flow direction is located vertically lower than a side having a smaller distance from the insert tube portion, and wherein, in at least a portion of a section, along the flow direction, of the tubular passage between the first tilted portion and the second tilted portion, a bottom end of a cross section, perpendicular to the flow direction, of the tubular passage is arranged vertically higher than a horizontal plane including a top end of an inner wall surface of the insert tube portion at a connection between the insert tube portion and the generator internal tube portion, the water supply tube being characterized in that the generator internal tube portion includes a connection tube portion and a tilted tube portion, the connection tube portion being tilted so that an end portion side connected to an upper horizontal tube portion is located vertically higher than an end portion side connected to the insert tube portion, and the tilted tube portion being tilted so that a side with an end portion connected to a horizontal ring tube portion is located vertically lower than a side with an end portion connected to the upper horizontal tube portion.