A method for determining core positions of an optical element array is provided, including the steps of causing white light to be incident on a first end face of an optical element of an optical element array including at least one optical element that is aligned and secured on a substrate, imaging light passing through the at least one optical element which is emitted from an opposed second end face of the at least one optical element using imaging means, and determining a core position of the at least one optical element based on a resulting image. The emitted light is imaged by the imaging means at an imaging distance where a diameter of the emitted light in the resulting image is as small as possible.