Abstract: To provide a random device for randomly testing logic circuits, particularly microprocessors, it is necessary to use a device for transforming the occurrence probability of logic vectors to produce vectors sequences having time-changing probabilities. Such a device comprises a memory or an equivalent circuit to which are applied input logic vectors (Ve1, Ve2 . . . Vn) having respective occurrence probabilities which are different or the same and containing, in the respective areas of different range, the different categories of output vectors (Vs1, Vs2 . . . Vsi). Thereby the occurrence probability of a predetermined output vector (Vs1, Vs2 . . . Vsi) depends both on the range of the memory area wherein said vector is stored, that is to say the number of elementary positions or eight-bit bytes which are included within said area, and on the respective probabilities (pr1, pr2 . . . prn) of the input vectors (Ve1, Ve2 . . . Ven) corresponding to the addresses of the elementary positions, m1, m2 . . .