PURPOSE: To provide a 2-cycle engine intake structure in which engine performance of the whole rotation range is improved, while compression ratio in a crank case is not reduced by making outflow of mixed air from side ends of lead valves smooth and increasing flow rate of mixed air so as to improve intake efficiency.

CONSTITUTION: A valve chamber 32 is formed in a crank case connected to an intake passage 34 and elastically deformable lead valves 37 are provided in valve mouths 36 of the upper and the lower face of a valve seat 35 of the lead valve device 33 provided in the valve chamber. The lead valve device 33 is attached to the connection part of an intake pipe 31 by a flange 39 at the base end part, gentle angle curved faces 40 which are expanded outward formed on both walls 32a of the valve chamber, expansion parts 41 are formed on these curved faces in a space toward both sides of the valve seat, projecting parts 42 are provided at required parts positions of both inner walls of the valve chamber opposed to both sidefaces of the valve seat on these expansion parts, and void between both sides of the valve seat and both inner walls of the vale chamber is made small by these projecting parts.