This sample injection device is provided with a plunger drive unit for driving a plunger by a pulse motor, an encoder for detecting an operating position of the pulse motor, and a control unit for adjusting a reference position of the tip end of the plunger with respect to the syringe based on the operating position detected by the encoder when the tip end of the plunger is brought into contact with the end portion in the syringe on the tip end side.