A gas pressure regulating valve (1; 1A-1V) comprising: a housing (12; 12A-12B; 12F-12H) including a valve passage connected to a primary port and a secondary port; a valve body (14; 14A-14N; 14S-14V) provided in the housing and configured to move between a closed position where the valve body closes the valve passage and an open position where the valve body opens the valve passage to adjust an opening degree of the valve passage; a return spring (26; 26G) configured to bias the valve body in a direction toward the closed position; and a valve body driving unit (17; 27; 27O; 27Q) configured to apply a driving force corresponding to an applied voltage or an applied current to the valve body against the biasing of the return spring to cause the valve body to move in a direction toward the open position, the gas pressure regulating valve being configured to regulate pressure of a high-pressure fuel gas, supplied through the primary port to the valve passage, to pressure corresponding to the driving force of the valve body driving unit to output the fuel gas through the secondary port, the gas pressure regulating valve comprising: a pressure return chamber (24; 24F; 24G) formed in the housing and connected to the secondary port; a first sealing member (19; 19F; 19G) configured to receive pressure of the pressure return chamber in a direction against the driving force and cause the valve body to move toward the closed position in accordance with the pressure of the pressure return chamber; a bearing member provided in a gap between the valve body and the housing and configured to slidingly support the valve body; and a second sealing member provided closer to the valve passage than the bearing member and configured to seal the gap; characterized by a third sealing member provided closer to the valve passage than the second sealing member and configured to seal the gap, wherein a buffer chamber (22; 22B; 22G; 22H) connected to the secondary port is formed between the third sealing member and the second sealing member. a housing (12; 12A-12B; 12F-12H) including a valve passage connected to a primary port and a secondary port; a valve body (14; 14A-14N; 14S-14V) provided in the housing and configured to move between a closed position where the valve body closes the valve passage and an open position where the valve body opens the valve passage to adjust an opening degree of the valve passage; a return spring (26; 26G) configured to bias the valve body in a direction toward the closed position; and a valve body driving unit (17; 27; 27O; 27Q) configured to apply a driving force corresponding to an applied voltage or an applied current to the valve body against the biasing of the return spring to cause the valve body to move in a direction toward the open position, the gas pressure regulating valve being configured to regulate pressure of a high-pressure fuel gas, supplied through the primary port to the valve passage, to pressure corresponding to the driving force of the valve body driving unit to output the fuel gas through the secondary port, the gas pressure regulating valve comprising: a pressure return chamber (24; 24F; 24G) formed in the housing and connected to the secondary port; a first sealing member (19; 19F; 19G) configured to receive pressure of the pressure return chamber in a direction against the driving force and cause the valve body to move toward the closed position in accordance with the pressure of the pressure return chamber; a bearing member provided in a gap between the valve body and the housing and configured to slidingly support the valve body; and a second sealing member provided closer to the valve passage than the bearing member and configured to seal the gap; characterized by a third sealing member provided closer to the valve passage than the second sealing member and configured to seal the gap, wherein a buffer chamber (22; 22B; 22G; 22H) connected to the secondary port is formed between the third sealing member and the second sealing member. a pressure return chamber (24; 24F; 24G) formed in the housing and connected to the secondary port; a first sealing member (19; 19F; 19G) configured to receive pressure of the pressure return chamber in a direction against the driving force and cause the valve body to move toward the closed position in accordance with the pressure of the pressure return chamber; a bearing member provided in a gap between the valve body and the housing and configured to slidingly support the valve body; and a second sealing member provided closer to the valve passage than the bearing member and configured to seal the gap; characterized by a third sealing member provided closer to the valve passage than the second sealing member and configured to seal the gap, wherein a buffer chamber (22; 22B; 22G; 22H) connected to the secondary port is formed between the third sealing member and the second sealing member.