PURPOSE: To provide high output performance by surely pointing scavenging flow inside a cylinder in the required flow direction.

CONSTITUTION: An air chamber 18 which functions as a distributing head of a scavenging air is formed in the lower part of a cylinder chamber 1 in such a way as surrounding its circumference in a two-cycle engine in which the scavenging air from a scavenging pump is supplied in a plural number of scavenging holes provided in the cylinder chamber. Scavenging passages 24, 25 are formed toward respective scavenging holes 2a-2e formed in the cylinder chamber 1 from this air chamber 18. Consequently, the scavenging flow direction toward the cylinder chamber 1 is surely pointed in the required flow direction.