The present invention relates to a pressure reducing apparatus. A diaphragm made from an elastic material is provided in the interior of a body. The diaphragm includes a main body portion having a seat member that is capable of being seated on an inner tubular member of the body, a retaining portion disposed on an outer peripheral side of the main body portion and which is slidably displaceable with respect to the inner tubular member, and a skirt that is retained on a flange of the body. Additionally, by flexing of the skirt by means of an elastic force of a spring, the seat member thereof separates away from the inner tubular member.