a pair of main bus lines spaced a predetermined distance apart from each other and disposed in substantially parallel to each other;

a plurality of diameters each comprising three circuit breaker units connected in series;

each of the circuit breaker units comprising a circuit breaker disposed in substantially parallel to axial directions of the main bus lines, and two disconnecting switches disposed in series in substantially parallel to the axial directions of the main bus lines so as to interpose the circuit breaker therebetween;

the circuit breaker including a hermetic vessel;

the disconnecting switches including hermetic vessels;

a first connection bus line interconnecting circuit breakers of adjacent circuit breaker units;

an auxiliary bus line;

second and third connection bus lines interconnecting the first auxiliary bus line and disconnecting switches arranged at ends of the gas-insulated switchgear device;

branch bus lines; and

first and second connection sections provided among the three circuit breaker units for the first and second connection bus lines and the branch bus lines;

wherein the branch bus lines are led out toward one of the main bus lines from the first connection section or being led out toward the other of the main bus lines from the second connection section so as to extend in a direction opposite to the leading-out direction of the branch bus lines from the first connection section; wherein axes of hermetic vessels of the circuit breakers are disposed at locations lower than axes of the first and second connection bus lines; wherein the disconnecting switches are disposed on the same axis as the first and second connection bus lines are disposed on; wherein the hermetic vessels of the circuit breakers and the hermetic vessels of the disconnecting switches are connected to each other; and wherein a space serving as at least one work space is provided under the second connection section; the work space having a length more than an axial length of hermetic vessels of the adjacent circuit breakers.