Liquid injection device for optically detecting a vial, aspirating a liquid in the vial with a syringe, and dispensing the liquid from the syringe

A liquid injection device for aspirating a liquid in a vial with a syringe and dispensing the liquid from the syringe to an injection destination, comprising:

• a mounting portion configured to mount the vial thereon;
• and
• a sensor having a light-emitting part and a light-receiving part, the sensor being configured to emit light from the light-emitting part to pass through at least a part of a cylindrical cap attached to the vial, and detect an amount of light received by the light-receiving part,
• wherein an optical axis of the light from the light-emitting part to the light-receiving part is shifted or inclined in a direction that increases a distance that the light passes through the cylindrical cap relative to a position where the optical axis of the light passes through a center axis of the cylindrical cap within a plane perpendicular to the center axis,
• wherein the optical axis is shifted within the plane perpendicular to the center axis of the cylindrical cap, and
• wherein the optical axis is shifted between a position where the optical axis passes through the center axis of the cylindrical cap within the plane perpendicular to the center axis of the cylindrical cap and a position where the optical axis passes through the cylindrical cap only once.