A pressure reducing valve comprising: a body in which a primary port and a secondary port are provided; a valve seat having an annular shape and a valve hole, the valve seat being provided in an intermediate portion of a gas passage that connects the primary port to the secondary port; a valve element provided upstream of the valve seat such that a gap is provided between the valve element and an inner peripheral surface of the gas passage, the valve element being configured to make contact with and move away from the valve seat; and a pressing mechanism configured to press the valve element in a direction in which the valve element moves away from the valve seat, in accordance with a pressure of the secondary port, wherein: the pressing mechanism includes a plug provided downstream of the valve seat and having a plug hole extending through the plug in an axial direction of the valve hole, and a pin including a sliding portion and an upstream end, the sliding portion having a shaft shape and being inserted in the plug hole such that a gap is provided between the sliding portion and an inner peripheral surface of the plug hole, and the upstream end being provided upstream of the sliding portion so as to contact the valve element; and the pin and the plug are provided such that a fitting length of the sliding portion with respect to the plug hole and the gap between the sliding portion and the plug hole satisfy a following expression: 0.0005 ⁢ L < C < 0.00908 ⁢ L, where L indicates the fitting length of the sliding portion with respect to the plug hole, and C indicates the gap between the sliding portion and the plug hole. a body in which a primary port and a secondary port are provided; a valve seat having an annular shape and a valve hole, the valve seat being provided in an intermediate portion of a gas passage that connects the primary port to the secondary port; a valve element provided upstream of the valve seat such that a gap is provided between the valve element and an inner peripheral surface of the gas passage, the valve element being configured to make contact with and move away from the valve seat; and a pressing mechanism configured to press the valve element in a direction in which the valve element moves away from the valve seat, in accordance with a pressure of the secondary port, wherein: the pressing mechanism includes a plug provided downstream of the valve seat and having a plug hole extending through the plug in an axial direction of the valve hole, and a pin including a sliding portion and an upstream end, the sliding portion having a shaft shape and being inserted in the plug hole such that a gap is provided between the sliding portion and an inner peripheral surface of the plug hole, and the upstream end being provided upstream of the sliding portion so as to contact the valve element; and the pin and the plug are provided such that a fitting length of the sliding portion with respect to the plug hole and the gap between the sliding portion and the plug hole satisfy a following expression: 0.0005 ⁢ L < C < 0.00908 ⁢ L, where L indicates the fitting length of the sliding portion with respect to the plug hole, and C indicates the gap between the sliding portion and the plug hole. the pressing mechanism includes a plug provided downstream of the valve seat and having a plug hole extending through the plug in an axial direction of the valve hole, and a pin including a sliding portion and an upstream end, the sliding portion having a shaft shape and being inserted in the plug hole such that a gap is provided between the sliding portion and an inner peripheral surface of the plug hole, and the upstream end being provided upstream of the sliding portion so as to contact the valve element; and a plug provided downstream of the valve seat and having a plug hole extending through the plug in an axial direction of the valve hole, and a pin including a sliding portion and an upstream end, the sliding portion having a shaft shape and being inserted in the plug hole such that a gap is provided between the sliding portion and an inner peripheral surface of the plug hole, and the upstream end being provided upstream of the sliding portion so as to contact the valve element; and the pin and the plug are provided such that a fitting length of the sliding portion with respect to the plug hole and the gap between the sliding portion and the plug hole satisfy a following expression: 0.0005 ⁢ L < C < 0.00908 ⁢ L, where L indicates the fitting length of the sliding portion with respect to the plug hole, and C indicates the gap between the sliding portion and the plug hole.