A breather device comprises a breather chamber (22) provided in a valve arm chamber (2) arranged above a cylinder head of an engine. In the breather chamber, blow-by gas including oil mist is separated into oil component and gas component, and the oil mist is removed from the blow-by gas. The interior of the breather chamber is alternately divided into plural horizontally juxtaposed rooms (22a, 22b, 22c) by a partition (23) extended from a bottom surface of the breather chamber and a partition (2a) extended from a ceiling surface of the breather chamber. Plural oil trap members (10) for trapping oil mist in the blow-by gas are arranged in the breather chamber. Especially, the oil trap member arranged at a blow-by gas inlet of the breather chamber is held by a holder (11) made separately from members (2, 7) forming the valve arm chamber (5).