Provided are a device and a method for pre-treating and injecting a liquid specimen. The device includes a first syringe comprising: a first tube having an open top and a first hole in the bottom; and protrusions formed in a lower and outer wall of the first tube; a second syringe comprising: a second tube having an open top and a second hole in the bottom and having an inner diameter greater than an outer diameter of the first tube; a second piston capable of moving along an inner wall of the second tube and having a third hole; and a communication channel providing a fluid communication between the first hole of the first tube and the third hole of the second piston and fixing the second piston to the first tube; and a joint portion being attachable to and detachable from a top of the second tube and having an opening having a shape which corresponds to a transverse cross-section of the first tube and grooves having a shape which corresponds to the shape of the protrusions such that the first tube can pass through the joint portion when the protrusions are matched with the grooves.