A continuous drug solution infusion device is provided that is capable of administering a drug solution into a patient's body for a predetermined period of time substantially at a predetermined flow rate from the beginning to end of the drug solution infusion by suppressing the change in pressure from the beginning to end of the infusion. The continuous drug solution infusion device has at least two tubular members disposed in series along an infusion path for a drug solution and at least one expandable/contractible tubular member disposed between the tubular members.