A pressure-reducing valve is disclosed which is capable of preventing leakage of a fluid from a passage aperture in a state in which the passage aperture is closed by a valve body. The pressure-reducing valve is structured such that a plunger is moved upward due to a biasing force of a shut spring when a magnetic field generated around and inside a solenoid body is released. Thus, the valve body is pushed up from below by a pressing portion of the plunger with a pressing force based on the biasing force of a shut spring. Due to the valve body being pushed up, the upper end of the valve body is placed in close contact with the inner peripheral portion of the passage aperture so that the passage aperture is closed. In this manner, leakage of hydrogen gas from a primary pressure chamber to a secondary pressure chamber (leakage of the gas pressure) can be prevented with certainty, and thus an unintentional increase of the pressure at the secondary pressure chamber side can be prevented with certainty.