A bleeder plug is provided with a bleeder body having a nipple portion and a threaded portion and being provided with a through hole extending from the nipple portion-side end to the threaded portion-side end; a seat pin having a press fitting portion to be press-fitted in an opening of the through hole at the threaded portion-side in the bleeder body and a seat portion blocking a bleeder hole, and a groove formed in a contact surface between the bleeder body and the seat pin and communicating the opening of the through hole at the nipple portion-side with an outside space via the contact surface.