A biosensor substrate includes a base substrate to which an excitation light beam is entered, a track formed on the base substrate, and a plurality of wells disposed on the base substrate and accommodating a specimen. A region on which the wells are disposed is sectioned into a plurality of zones in a radial direction, and the wells are arranged on the zones in a circumferential direction. The biosensor substrate is driven at a constant angular velocity while a zone is scanned with the excitation light beam. Velocities set to the zones are varied between the zones, and a zone on the outer radial side has a smaller angular velocity.