PURPOSE: To provide a breather device wherein a breather can be arranged without forming any hole on a casing, and lubricating oil is not leaked to the outside even if a rotational part such as a gear is rotated at high speed by adopting the simple structure.

CONSTITUTION: In a breather wherein a breather passage 4 formed by an axial thin hole to be communicated with the inside and the outside of a casing is provided on the shaft core of a rotary shaft 3 journalled by penetrating a casing 6, a presser plate 1 wherein radial breather grooves 2 are formed on an end surface 5 on the casing inside of the rotary shaft 3 so as to be communicated. with the breather passage 4, drops of lubricating oil are returned into the casing by air flow generated by the pump action of the radial breather grooves 2 when the rotary shaft 3 is rotated.