Abstract: A first sensor (13-1), the mounting position of the first sensor (13-1) being recognized as a counting number of instruction pulses to a pulse motor (3), is arranged along a plate (11) with slits of an encoder at a portion between a position where a pushing holder (7) is connected to a plunger (9) for the liquid infusion, and a start position where the pushing holder (7) is separated from the plunger (9). A counting means (16) for counting encoder pulses from the encoder, is reset when a first sensor (13-1) is detected by a position detecting device (14) moved together with the pushing holder (7), and started to count the encoder pulses according to the movement of the pushing holder (7). A time to complete the liquid infusion is calculated by using a distance between the position where the plunger (9) is connected to the holder (7) and a liquid infusion finish position proper to the syringe, and a predetermined liquid infusion speed.