PURPOSE: To adjust a pulse interval corresponding to each channel of an A & B code transmission circuit with high reliability by an easy and inexpensive method by allowing a variation of capacitance of a capacitor deciding an inverting period of a multivibrator circuit to be adjusted by one variable resistor independently of number of channels.

CONSTITUTION: C is the capacitance value of the capacitor 28 and four kinds of inverting periods (t1<t2<t3<t4) are formed. C' is the minimum value of the variation in the capacitance and a resistance value forming a desired inverting period with the said capacitance variation is obtained. The inverting period (t) of the multivibrator circuit is expressed as 0.69CR in general. Then a resistor R1 with the inverting period t1 in the minimum capacitance variation is obtained as t1/0.69C'. Resistors R2, R3 and R4 with periods t2, t3 and t4 are obtained similarly. Adjacent resistance differences Δr1∼ Δr3 of the R1∼R4 are obtained respectively and the resistors each having values of R1, Δr1, Δr2, Δr3 are connected in series. In forming the period t1, the resistors Δr1, Δr2 and Δr3 are short-circuited. In forming the periods t2, t3, t4, it is conducted similarly. Resistors 29∼32 in figure correspond respectively to the resistance values above. The periods t3, t2 and t1 are formed with high accuracy by adjusting a variable resistor 26 with the state above so as to adjust the t4 into the desired inverting period.