According to the present invention, a device body casing 17 has a liquid chamber 20a for temporarily storing a liquid to be transported by a pump, a gas chamber 20b, and an extendably and contractibly deformable pulsation suppression diaphragm 18, which separate them. The device body casing 17 having an aperture 27 so as to communicate with gas chamber 20b, is detachably engaged with a valve case 23. The valve case 23 is provided with an automatic gas supply valve mechanism 33 and an automatic gas exhaust valve mechanism 34, which restrict the amount of the extendable and contractible deformation of the pulsation suppression diaphragm 18 within the predetermined range, so that a liquid pressure inside the liquid chamber 20a and an atmospheric pressure inside the gas chamber 20b may balance each other when the discharge pressure of the pump is fluctuated. The automatic gas exhaust valve mechanism 34 is provided with a gas exhaust port 32, a gas exhaust valve element 43, and a slider 48. The gas exhaust port 32 exhausts the gas from the gas chamber 20b to the outside, when the gas sealing pressure inside the gas chamber 20b is decreased. The gas exhaust valve element 43 usually makes the gas exhaust port 32 close. The slider 48 is operated so that the gas exhaust valve element 43 may usually make the gas exhaust port 32 open, when the pulsation suppression diaphragm 18 is moved in a direction of reducing the liquid chamber 20a so as to exceed the predetermined stroke. The gas exhaust valve element 43 is disposed on a tip of the gas exhaust valve rod 45. A rear end of the gas exhaust valve rod 45 is slidably inserted in the slider 48. The gas exhaust valve rod 45 is loosely inserted in a through hole 46 of the spring receiving member 47 fixed to the inside of the gas exhaust chamber 42 of the valve case 23. On the gas exhaust rod 45, a spring 49 for a closing state is disposed between the gas exhaust valve element 43 and the spring receiving member 47, and a spring 50 for an opening state is disposed between the spring receiving member 47 and the slider 48.