PURPOSE: To provide a gas insulated switchgear in which the function stop interval of a switchyard is shortened while enhancing the capacity of a power supply facility.

CONSTITUTION: A power transaction current transformer 10 is connected with a protective current transformer 14 through a T-type connection bus 1. The T-type connection bus 1 has a third tap part 1a terminated by a metal cover 2 under normal operating conditions of a gas insulated switchgear. When the power transaction current transformer is tested, the metal cover 2 at the third tap part 1a of the T-type connection bus 1 is replaced by a three-phase short- circuiting bus 4 for short-circuiting the high voltage conductors in the connection bus 1 at the same part. A test current applying wire is connected, in place of a transmission line 16, with a bushing 15 and the test current applying wire is also connected with bushings 8 of other phases through a measuring current transformer and a conducting current transformer.