PURPOSE: To keep the exhaust timing accurately by preventing exhaust gas leakage from between an exhaust port and an exhaust timing control valve as well as to keep engine constitution simply even if an exhaust device is juxtaposed.

CONSTITUTION: In an exhaust timing control device 16 of a two-cycle engine 1 having an exhaust timing control valve 17 to vary a height of an upper dead center side end part of an exhaust port 14 opening on an inner wall surface of a cylinder bore 5, The exhaust timing control valve 17 is constituted in a cylindrical rotor shape so as to be rotatable freely with a rotary shaft C along a central shaft B of the exhaust port 14 as its center while crossing at a right angle to a central shaft A of the cylindr bore 5. An exhaust communicating hole 29 is bored to vary the height of the upper dead center side end part of the exhaust port 14 according to a turning angle of the exhaust timing control valve 17, and a driving means 18 to drive the exhaust timing control valve 17 in rotation and a control means 18 to change the exhaust timing by operating the driving means 18 when an engine reaches the prescribed number of revolutions, are provided.