In an accumulator comprising a pressure vessel, a bellows dividing the interior of the pressure vessel into a gas chamber filled with pressurized gas and a liquid chamber which communicates with a liquid pressure circuit via a liquid introduction port, a stay member attached to the inner surface of the pressure vessel inside the bellows and provided with a communication port for communicating the interior and exterior of the stay member with each other and adapted to be closed by a part of the bellows to define a fully contracted state of the bellows, and a safety valve provided in the stay member, typically in the form of a weakened portion of the stay member, for selectively communicating the exterior of the stay member with the interior of the stay member. Thus, because the safety valve is not provided in the pressure vessel itself, the safety valve of the present invention would not affect the sealing capability of the pressure vessel.