Safety device for a pressurized gas tank, comprising: - a support body intended to be fixed to the containment wall of a tank, and internally delimiting an evacuation channel, which is intended to place the internal volume of the tank in flow connection with the external environment; - a shutter placed to intercept said evacuation channel, extended along a main extension axis and movable between: - a closed position, in which said shutter is placed to close said evacuation channel in order to hydraulically separate the interior of the tank from the external environment; - an open position, in which said shutter at least partially frees said evacuation channel, in order to allow the pressurized gas contained in the tank to exit towards the external environment; said shutter being provided with: - a shaft extended along said main extension axis and at least partially inserted within said evacuation channel; - a closure head placed at a first end of said shaft intended to be directed towards the external environment; - a spring wound around said shaft and interposed between said support body and a contrast element fixed to a second end of said shaft intended to be directed inside the tank, said spring being adapted to force the closure head of said shutter into said closed position; - a fusible element; said safety device being characterized in that: - said closure head comprises a hollow sleeve provided with a through hole slidably traversed by said shaft and delimiting a housing space in which said fusible element is housed; - said shutter comprises a retention element, which is fixed to said shaft at said first end, and is pulled by said spring against said fusible element. - a support body intended to be fixed to the containment wall of a tank, and internally delimiting an evacuation channel, which is intended to place the internal volume of the tank in flow connection with the external environment; - a shutter placed to intercept said evacuation channel, extended along a main extension axis and movable between: - a closed position, in which said shutter is placed to close said evacuation channel in order to hydraulically separate the interior of the tank from the external environment; - an open position, in which said shutter at least partially frees said evacuation channel, in order to allow the pressurized gas contained in the tank to exit towards the external environment; said shutter being provided with: - a shaft extended along said main extension axis and at least partially inserted within said evacuation channel; - a closure head placed at a first end of said shaft intended to be directed towards the external environment; - a spring wound around said shaft and interposed between said support body and a contrast element fixed to a second end of said shaft intended to be directed inside the tank, said spring being adapted to force the closure head of said shutter into said closed position; - a closed position, in which said shutter is placed to close said evacuation channel in order to hydraulically separate the interior of the tank from the external environment; - an open position, in which said shutter at least partially frees said evacuation channel, in order to allow the pressurized gas contained in the tank to exit towards the external environment; - a shaft extended along said main extension axis and at least partially inserted within said evacuation channel; - a closure head placed at a first end of said shaft intended to be directed towards the external environment; - a spring wound around said shaft and interposed between said support body and a contrast element fixed to a second end of said shaft intended to be directed inside the tank, said spring being adapted to force the closure head of said shutter into said closed position; - a fusible element; - said closure head comprises a hollow sleeve provided with a through hole slidably traversed by said shaft and delimiting a housing space in which said fusible element is housed; - said shutter comprises a retention element, which is fixed to said shaft at said first end, and is pulled by said spring against said fusible element.