A pressure regulating device, which is adapted to be connected to an outlet opening of a portable gas tank, comprising: a pressure stabilizer comprising a valve body, a pressure regulating assembly, and a switching assembly, wherein the valve body has an inlet portion, a decompression chamber, and an outlet portion; the inlet portion has an inlet port adapted to be connected to the outlet opening of the portable gas tank; the decompression chamber communicates with the inlet portion; the outlet portion communicates with the decompression chamber; the outlet portion has an outlet port; the pressure regulating assembly is disposed in the decompression chamber and is adapted to regulate a pressure of a gas outputted by the portable gas tank to form an output gas with a predetermined pressure; the switching assembly is disposed in the outlet portion, and is located between the decompression chamber and the outlet port, and is manipulable to block or open the output gas, characterized in that the outlet portion has a receiving chamber; a wall of the receiving chamber has a side opening communicating with the decompression chamber; the switching assembly comprises a plug member located in the receiving chamber; the plug member has a through hole located at a radial direction of the plug member and an axial hole communicating with the through hole and the outlet port; the plug member is turnable between a first position (P 1) and a second position in an axial direction of the plug member; when the plug member is at the first position, an outer peripheral surface of the plug member closes the side opening; when the plug member is at the second position, the through hole communicates with the side opening; a manipulating member has a connecting end and has a gas passage therein; an end of the gas passage forms an inlet at the connecting end, and another end of the gas passage is adapted to communicate with a gas pipe; the manipulating member is detachably connected to the outlet port via the connecting end; the connecting end is connected to the plug member, and the gas passage communicates with the axial hole; the manipulating member drives the plug member to turn between the first position and the second position. a pressure stabilizer comprising a valve body, a pressure regulating assembly, and a switching assembly, wherein the valve body has an inlet portion, a decompression chamber, and an outlet portion; the inlet portion has an inlet port adapted to be connected to the outlet opening of the portable gas tank; the decompression chamber communicates with the inlet portion; the outlet portion communicates with the decompression chamber; the outlet portion has an outlet port; the pressure regulating assembly is disposed in the decompression chamber and is adapted to regulate a pressure of a gas outputted by the portable gas tank to form an output gas with a predetermined pressure; the switching assembly is disposed in the outlet portion, and is located between the decompression chamber and the outlet port, and is manipulable to block or open the output gas, characterized in that the outlet portion has a receiving chamber; a wall of the receiving chamber has a side opening communicating with the decompression chamber; the switching assembly comprises a plug member located in the receiving chamber; the plug member has a through hole located at a radial direction of the plug member and an axial hole communicating with the through hole and the outlet port; the plug member is turnable between a first position (P 1) and a second position in an axial direction of the plug member; when the plug member is at the first position, an outer peripheral surface of the plug member closes the side opening; when the plug member is at the second position, the through hole communicates with the side opening; a manipulating member has a connecting end and has a gas passage therein; an end of the gas passage forms an inlet at the connecting end, and another end of the gas passage is adapted to communicate with a gas pipe; the manipulating member is detachably connected to the outlet port via the connecting end; the connecting end is connected to the plug member, and the gas passage communicates with the axial hole; the manipulating member drives the plug member to turn between the first position and the second position.