An interface device for coupling a payment card to an electronic device so as to allow the electronic device to access the payment card via said interface device, said interface device including: a housing; a switching unit movably connected to said housing; a circuit board mounted on said switching unit and brought to move relative to said housing by said switching unit; a card interface including a card terminal set disposed on said circuit board; and a first connecting interface configured to be electrically connected to a first socket of the electronic device, and including a first terminal set disposed on said circuit board and a first shell member connected to said switching unit and surrounding said first terminal set and said card terminal set, said first shell member and said circuit board cooperating to define a card slot for containing said payment card therein such that said payment card is electrically connected to said card terminal set; wherein said interface device is operable to switch between a retracted state, in which said first connecting interface is contained in said housing, and an exposed state, in which said first connecting interface protrudes from said housing; wherein: said housing has an elongated shape with a pair of long sides, each of said long sides being formed with an opening (201, 202); said switching unit is rotatably disposed in said housing; said circuit board has an elongated shape with a pair of short sides, one of which being provided with said first connecting interface; when said interface device is in the retracted state, said circuit board is substantially parallel to said housing, containing said connecting interface in said housing; and when said interface device is in the exposed state, said circuit board is substantially perpendicular to said housing, resulting in said first connecting interface extending out of said housing through one of said openings. a housing; a switching unit movably connected to said housing; a circuit board mounted on said switching unit and brought to move relative to said housing by said switching unit; a card interface including a card terminal set disposed on said circuit board; and a first connecting interface configured to be electrically connected to a first socket of the electronic device, and including a first terminal set disposed on said circuit board and a first shell member connected to said switching unit and surrounding said first terminal set and said card terminal set, said first shell member and said circuit board cooperating to define a card slot for containing said payment card therein such that said payment card is electrically connected to said card terminal set; wherein said interface device is operable to switch between a retracted state, in which said first connecting interface is contained in said housing, and an exposed state, in which said first connecting interface protrudes from said housing; wherein: said housing has an elongated shape with a pair of long sides, each of said long sides being formed with an opening (201, 202); said switching unit is rotatably disposed in said housing; said circuit board has an elongated shape with a pair of short sides, one of which being provided with said first connecting interface; when said interface device is in the retracted state, said circuit board is substantially parallel to said housing, containing said connecting interface in said housing; and when said interface device is in the exposed state, said circuit board is substantially perpendicular to said housing, resulting in said first connecting interface extending out of said housing through one of said openings. said housing has an elongated shape with a pair of long sides, each of said long sides being formed with an opening (201, 202); said switching unit is rotatably disposed in said housing; said circuit board has an elongated shape with a pair of short sides, one of which being provided with said first connecting interface; when said interface device is in the retracted state, said circuit board is substantially parallel to said housing, containing said connecting interface in said housing; and when said interface device is in the exposed state, said circuit board is substantially perpendicular to said housing, resulting in said first connecting interface extending out of said housing through one of said openings.