Abstract: A constant flow valve comprising a valve casing having a flow passage having a curve due to a partition arranged between an inlet flow passage and an outlet flow passage, a chamber located above and between the inlet flow passage and the outlet passage, and an opening communicating the inlet flow passage with the chamber and tapered from the downstream side toward the upstream side; a cap attached to the valve casing and supporting a cylinder arranged coaxially with the opening and able to move forward and backward, and having a sealing surface at the lower end thereof which is pressed against a valve seat of the opening; a valve plug slidably fitted in the cylinder and having a through hole communicating with the opening, and arranged coaxially with the opening so that an orifice is always defined between the opening and the end of the valve plug; and a spring arranged between the valve plug and the cylinder, to bias the valve plug away from the opening.