Yukawa's bi-local field is investigated as a simple model for an extended particle and is quantized so as to represent the Regge pole behaviour. Two characteristic aspects of elastic scattering at high energies, the diffraction pattern near the forward direction and the compound elastic type of scattering at large angle are explained in a unified way, i.e. the former is explained by the exchange of this extended particle with a space-like four-momentum and the latter by the occurrence of this particle with a time-like four-momentum in the intermediate state of scattering. The difference is emphasized which is due to whether the particle under consideration propagates with a space-like or a time-like four-momentum, in reference to the validity of Fierz's expansion postulate on Yukawa's bi-local field.