To provide a practical switch circuit which can connect a load circuit to an AC power source without causing any electrical transient phenomenon.

A method for connecting an AC power source S having an already fixed output to a load as a function of time in a power system. (a) In the above-mentioned power system, electric power is supplied to the load at a first power value so as to form a certain electrical state. (b) During or after the above-mentioned process, the electrical state is detected. (c) In the above-mentioned system, the connecting timing of the power source to the load is decided. (d) The power source S is connected to the load so that electric power can be supplied to the load at a second power value which is considerably larger than the first power value in accordance with the timing decided through the process described in (c) above.