PURPOSE: To carry out a complete suction process by closing in the suction passage between a gas detection tube and a bellows inner chamber in the direction of the bellows inner chamber, operating a grip plate and providing an openable suction valve in a complete sample sampling path.

CONSTITUTION: A bellows pump comprises a bellows 1, grip plates 2, 3, which are formed through a scissor-like link mechanism 4 in parallel. Two spiral springs 5 are disposed in the inside of the bellows 1, and a discharge valve 6 and a suction valve 10 are provided on the grip plates 2, 3 respectively. Furthermore, a gas detection tube 8 and a visual sensation display 11 are provided on the grip plate 3. Here, when the grip plates 2, 3 are incompletely pressed and matched, initial air flow heightened at the time of releasing is produced in a short time, the valve 10 is closed and gas flow is blocked. And when the grip plates 2, 3 are completely pressed and matched, the valve 10 is held in an open state, while a pressure transmission process is performed, the valve 10 is held at an automatically opened position, and a complete suction process can be carried out.