<p>A medical fluid infusing device capable of minimizing the quantity of infused contrast medium with a simple structure while adequately maintaining the contrast. Lower limit storage means (134) stores the lower limit rate inputted into lower limit input means (133), and start detecting means (135) detects rate decrease start. Action control means (140) maintains the infusion rate of a piston drive mechanism (117) at a reference rate until a rate decrease starts and decreases the infusion rate to the stored lower limit rate when the rate decrease starts. Therefore, it is possible to maintain the rate of infusion of the contrast medium at a reference rate until the contrast reaches an appropriate value and to decrease the rate to a lower limit rate after the contrast reaches the appropriate value.</p>
