Provided is a through-focus image-based metrology device including an optical device, and a computing device configured to acquire at least one through-focus image of a target from the optical device, generate an intensity profile based on the acquired at least one through-focus image, and perform metrology on the target based on the generated intensity profile, wherein the optical device includes a stage on which the target is disposed, the stage being configured to move by one step in at least one direction based on control of the computing device, and to acquire the at least one through-focus image, an image sensor disposed on the stage, an objective lens disposed between the image sensor and the stage, the objective lens being configured to transmit reflected light from the target, and a light source configured to emit illumination light to the target through the objective lens.