An approach for implementing a fuzzy inference system by the use of beam-scanning laser diodes is reported. Configurations of the inference system are proposed, and basic experiments of each processing unit are described. The feasibility of the inference technique is also discussed. A PRODUCT-SUM-gravity method of the inference technique is used instead of a conventional min-max-gravity method. Numerical simulation indicates that the PRODUCT-SUM-gravity method leads to higher controllability than the min-max-gravity method. A Gaussian that uses a far-field pattern of a laser diode is an envelope of the membership function. Features of optics, such as scanning the far-field beam and finding the center of gravity of an optical field, are used in the inference processes. Inference speed of the system is faster than several tens of mega-Flips (fuzzy logical inference per second) when one processing unit is used.