A bellows pump device includes first and second bellows mounted on a pump head so as to be expandable/contractible independently of each other and configured to suck a fluid from a suction passage thereinto by expansion thereof and discharge the fluid therefrom to a discharge passage by contraction thereof. First and second air cylinder portions are configured to respectively cause the first and second bellows to perform expansion/contraction operation. First and second detection devices are configured to detect expanded/contracted states of the first and second bellows, respectively. A control unit is configured to control drive of the first and second air cylinder portions on the basis of each of detection signals of the first and second detection devices such that, before one bellows comes into a most contracted state, the other bellows is caused to contract from a most expanded state.