Abstract: Disclosed is a detecting device for hit determination by detecting a light shot from a transmitter. The detecting device according to the invention comprises a plurality of detecting elements. Each detecting element includes an optical detector cell of a planar shape for generating an electric signal when detecting a light, a protection case of a cylindrical shape for supporting the optical detector cell housed inside thereof, a set of lead wires, each of which being electrically connected to an anode electrode and a cathode electrode of the optical detector cell for supplying the electric signal generated from the optical detector cell to hit determination means, and a protection shield located on a front light detecting surface of the optical detector cell for protecting the optical detector cell from external environment and passing the light. The protection case of a cylindrical shape has an open front surface.