In the analog circuits for the systms governed by the dilfercntial equations with the coefficients which are a function of one or mOre of the dependent variables, the magnitudes of their circuit elements must be variable in accordance with the nature of the function. Such circuit elements can be realized by means of inserting or removing the additional elements with high speed switches in the analog circuits. Particularly, in the case of varying stepwise this method is effective. But as an analog circuit is regarded as a short-time or repetitive type analyzer, the above switches must be instantaneous operation. In this paper, first, it is made sure by the experiments that some of the transistor switches arc met this condition, and moreover arc very low closed resistance, very high open resistance and neglegible small voltage offsets. Next, the basic technique for the direct analog simulation usiug transistor switches is described about the simple example, i.e. the oscillatory system with varying cross-scctional surge tank. Finally, as its applications, the transient problems of these oscillatory systems arc solved by means of these analog circuits.