PURPOSE: To improve the output by enhancing the inertia intake effect during low-speed operation while securing the intake air quantity during medium-high speed operation in an engine.

CONSTITUTION: An intake port of a 3-intake valve engine comprises one inlet part 11 and three outlet parts 12, 13, 14 which are communicated with one inlet part 11 and formed in such a manner that the sectional areas thereof are substantially the same. When the long diameter of the inlet part 11 is taken to be (a), the distance between the centers of the outlet parts 12, 14 positioned on both sides is taken to be (w), and the shaft diameter of an intake valve disposed in the outlet parts 12, 14 is taken to be (d), a partition wall 16 is formed to the adjacent outlet parts 12, 13, 14 in the intake port having the relation expressed by the equation: a≥w-d.