Minimally invasive surgery has recently become a key word in medical engineering. In this operation, to introduce surgical instruments, spatulas which push tissues aside and retain the approach path to the affected area as well as workspace for the insertion of such instruments are necessary. Therefore, a new type of hydraulically-driven flexible manipulator for neurosurgery has been developed. With an attached balloon and using only physiological saline for the drive system, safety of the brain tissue, especially in terms of pressure, is assured as is the simplicity of the mechanism. In addition, this provides the advantage of MRI compatibility. From the results of several evaluations, this manipulator has been proved effective as a new type of medical device.