A gas-insulated switchgear device, comprising: - a supporting structure having a base adapted for placement on a supporting surface; - one or more poles, each pole of said one or more poles comprising a first casing housing at least a first terminal and a second terminal for input/output connection; - a disconnector unit comprising at least a first fixed contact operatively coupled to said first terminal and a corresponding first movable contact which can be electrically connected/disconnected with/from said first fixed contact during operation of the disconnector unit, and a second fixed contact operatively coupled to said second terminal and a corresponding second movable contact which can be electrically connected/disconnected with said second fixed contact during operation of the disconnector unit; - a circuit breaker unit electrically connected to said disconnector unit and having at least a couple of interruption contacts (10,11) which can be actuated along a longitudinal reference axis during operation of said circuit breaker unit between a circuit breaker closed position where they are electrically coupled and a circuit breaker open position where they are electrically separated; characterized in that each of said one or more poles is mounted on said supporting structure with said longitudinal reference axis transversal with respect to the supporting surface, and in that said first casing comprises at least a first porthole for visually checking the position of said first movable contact and a second porthole spaced apart from said first porthole for visually checking the position of said second movable contact, wherein said at least first porthole and said first terminal are positioned substantially opposite to each other with respect to said reference axis, and wherein said second porthole and said second terminal are positioned substantially opposite to each other with respect to said reference axis. - a supporting structure having a base adapted for placement on a supporting surface; - one or more poles, each pole of said one or more poles comprising a first casing housing at least a first terminal and a second terminal for input/output connection; - a disconnector unit comprising at least a first fixed contact operatively coupled to said first terminal and a corresponding first movable contact which can be electrically connected/disconnected with/from said first fixed contact during operation of the disconnector unit, and a second fixed contact operatively coupled to said second terminal and a corresponding second movable contact which can be electrically connected/disconnected with said second fixed contact during operation of the disconnector unit; - a circuit breaker unit electrically connected to said disconnector unit and having at least a couple of interruption contacts (10,11) which can be actuated along a longitudinal reference axis during operation of said circuit breaker unit between a circuit breaker closed position where they are electrically coupled and a circuit breaker open position where they are electrically separated; characterized in that each of said one or more poles is mounted on said supporting structure with said longitudinal reference axis transversal with respect to the supporting surface, and in that said first casing comprises at least a first porthole for visually checking the position of said first movable contact and a second porthole spaced apart from said first porthole for visually checking the position of said second movable contact, wherein said at least first porthole and said first terminal are positioned substantially opposite to each other with respect to said reference axis, and wherein said second porthole and said second terminal are positioned substantially opposite to each other with respect to said reference axis.