PURPOSE: To obtain a reliability value derivation system of inference chain by providing a circuit generating an inference block and the smaller one of two input signals as the output, a storage cell and a switch for processing the inference chain while inspecting each inference in a chain successively.

CONSTITUTION: In a fuzzy syllogism inference device, it functions so that an analog signal where the amplitude becomes the measured value of a certainty degree in the final major premise in an inference chain may be generated at an output 112. The true value as analog between 0 and 1 in a small premise A are supplied to the negative input of two input location switches 41. The upper sides of the switches closes down the feedback rounte from the positive output of an inference block 41 generating a desired inference output to the negative input of the inference block 41. The true values of the major premise of chains A→B, B→C, C→D are successively supplied to the positive input terminal of the inference block 41 under the control of a clock signal 44. The clock signal 44 is used for controlling various kinds of clock storage cells 45, 46, 47 and a switch 43.