The present invention provides a medical liquid injection device which is configured so as to accurately obtain the position of an end of the piston to thereby perform desired operation. A medical liquid injection device (100) has: a piston drive mechanism (130) provided with a piston pressing unit which presses an end of the piston of a held syringe in order to move forward the piston and a proximity sensor (132) which detects the distance between the piston and the piston pressing unit. The operation of the piston pressing unit is controlled so that, on the basis of the result of detection of the distance by the proximity sensor (132), the movement speed of the piston pressing unit is reduced in the last predetermined section of preparatory operation in which the piston pressing unit is moved from the initial position until the piston pressing unit is in contact with the end of the piston.
