Bellows pump apparatus

Provided is a bellows pump apparatus by which an impulsive pressure generated when being switched from suctioning to discharging an operating fluid can be easily suppressed even in a pre-installed bellows pump. The bellows pump apparatus suctions a fluid to be transferred, by supplying one air chamber (26) of two sealed air chambers (21, 26) with pressurized air to expand bellows (13, 14); and discharges the fluid to be transferred, by supplying the other air chamber (21) with pressurized air to contract the bellows (13, 14). This bellows pump apparatus is provided with: electro-pneumatic regulators (51, 52) for adjusting a first air pressure of the pressurized air supplied to the one air chamber (26) and a second air pressure of the pressurized air supplied to the other air chamber (21); and a control unit (6) for controlling the electro-pneumatic regulators (51, 52) such that the first air pressure becomes smaller than the second air pressure at least at the time when expansion is ended during expansion of