An internal combustion engine intake port structure comprising: a cylinder forming a combustion chamber; two intake openings (511, 512) opening at a ceiling surface of the combustion chamber and arranged next to each other in an engine output axis direction on one side with respect to the engine output axis when the combustion chamber is viewed in a cylinder axis direction; a first intake port connected to one of the two intake openings (511, 512); a second intake port connected to the other one of the two intake openings (511, 512) and arranged next to the first intake port in the engine output axis direction; and intake valves (16, 17) each provided at the first intake port and the second intake port and configured to open or close the intake openings (511, 512) at substantially identical timing, wherein each intake valve (16, 17) includes a shaft portion (161, 171) reciprocating up and down, and a shade portion (162, 172) connected to a lower end portion of the shaft portion (161, 171) and configured to contact the intake opening (511, 512) from an inner side of the combustion chamber to close the intake opening (511, 512), when the intake valves (16, 17) each open the corresponding intake openings (511, 512), a downstream end portion of the first intake port and a downstream end portion of the second intake port extend, as viewed in a section perpendicular to the engine output axis, to direct to between a shade back (162a, 172a) of the shade portion (162, 172) positioned on a cylinder axis side with respect to the shaft portion (161, 171) and the ceiling surface facing the shade back (162a, 172a), at an inner wall surface of a second intake port side portion, which is located on the downstream end portion of the first intake port, in a case where the downstream end portion of the first intake port is, as viewed in a section perpendicular to a cylinder axis, divided into a second intake port side and an opposite second intake port side, an orientation surface for directing, in a direction toward the opposite second intake port side in the combustion chamber, a flow of gas flowing toward the combustion chamber along the inner wall surface is formed, and characterized in that as viewed in a section perpendicular to a direction from an upstream side to a downstream side of the first intake port, the orientation surface curves apart from the second intake port in a direction from the other side with respect to the engine output axis to the one side as compared to a shape of an inner wall surface of an opposite second intake port side portion mirror-reversed to the second intake port side. a cylinder forming a combustion chamber; two intake openings (511, 512) opening at a ceiling surface of the combustion chamber and arranged next to each other in an engine output axis direction on one side with respect to the engine output axis when the combustion chamber is viewed in a cylinder axis direction; a first intake port connected to one of the two intake openings (511, 512); a second intake port connected to the other one of the two intake openings (511, 512) and arranged next to the first intake port in the engine output axis direction; and intake valves (16, 17) each provided at the first intake port and the second intake port and configured to open or close the intake openings (511, 512) at substantially identical timing, wherein each intake valve (16, 17) includes a shaft portion (161, 171) reciprocating up and down, and a shade portion (162, 172) connected to a lower end portion of the shaft portion (161, 171) and configured to contact the intake opening (511, 512) from an inner side of the combustion chamber to close the intake opening (511, 512), when the intake valves (16, 17) each open the corresponding intake openings (511, 512), a downstream end portion of the first intake port and a downstream end portion of the second intake port extend, as viewed in a section perpendicular to the engine output axis, to direct to between a shade back (162a, 172a) of the shade portion (162, 172) positioned on a cylinder axis side with respect to the shaft portion (161, 171) and the ceiling surface facing the shade back (162a, 172a), at an inner wall surface of a second intake port side portion, which is located on the downstream end portion of the first intake port, in a case where the downstream end portion of the first intake port is, as viewed in a section perpendicular to a cylinder axis, divided into a second intake port side and an opposite second intake port side, an orientation surface for directing, in a direction toward the opposite second intake port side in the combustion chamber, a flow of gas flowing toward the combustion chamber along the inner wall surface is formed, and characterized in that as viewed in a section perpendicular to a direction from an upstream side to a downstream side of the first intake port, the orientation surface curves apart from the second intake port in a direction from the other side with respect to the engine output axis to the one side as compared to a shape of an inner wall surface of an opposite second intake port side portion mirror-reversed to the second intake port side.