A portable electronic device comprising: first and second device units (10,20); and at least one hinge assembly (100A,100B) configured to pivotably connect the second device unit to the first device unit, the hinge assembly (100A,100B) comprising: a first fixing unit fixed to the first device unit; a second fixing unit fixed to the second device unit; a plurality of shaft members (130,140,150,160,170,180) arranged in parallel with one another, the plurality of shaft members (130,140,150,160,170,180) comprising first and second outer shaft members (130,180) respectively mounted on the first and second fixing units (110,120), and a plurality of inner shaft members (140,150,160,170) arranged between the first and second outer shaft members (130,180); a gear unit mounted on the plurality of shaft members (130,140,150,160,170, 180) and configured to connect the plurality of shaft members (130,140,150,160,170,180) with one another through a gear mesh; and wherein the hinge assembly (100A,100B) further comprises a plurality of coupler members (330,340,350,360,370), wherein any two neighbouring shaft members (130,140, 150,160,170,180) are connected to each other by one of the plurality of coupler members (330,340,350,360,370) which are disposed on an opposite side to the gear unit with reference to the first fixing unit and the second fixing unit in order to maintain consistent intervals between the plurality of shaft members (130,140,150,160,170,180); and wherein each of the coupler members (330,340,350,360,370) and the gear unit is mounted on the shaft members (130,140,150,160,170,180) passing through them. first and second device units (10,20); and at least one hinge assembly (100A,100B) configured to pivotably connect the second device unit to the first device unit, the hinge assembly (100A,100B) comprising: a first fixing unit fixed to the first device unit; a second fixing unit fixed to the second device unit; a plurality of shaft members (130,140,150,160,170,180) arranged in parallel with one another, the plurality of shaft members (130,140,150,160,170,180) comprising first and second outer shaft members (130,180) respectively mounted on the first and second fixing units (110,120), and a plurality of inner shaft members (140,150,160,170) arranged between the first and second outer shaft members (130,180); a first fixing unit fixed to the first device unit; a second fixing unit fixed to the second device unit; a plurality of shaft members (130,140,150,160,170,180) arranged in parallel with one another, the plurality of shaft members (130,140,150,160,170,180) comprising first and second outer shaft members (130,180) respectively mounted on the first and second fixing units (110,120), and a plurality of inner shaft members (140,150,160,170) arranged between the first and second outer shaft members (130,180); a gear unit mounted on the plurality of shaft members (130,140,150,160,170, 180) and configured to connect the plurality of shaft members (130,140,150,160,170,180) with one another through a gear mesh; and wherein the hinge assembly (100A,100B) further comprises a plurality of coupler members (330,340,350,360,370), wherein any two neighbouring shaft members (130,140, 150,160,170,180) are connected to each other by one of the plurality of coupler members (330,340,350,360,370) which are disposed on an opposite side to the gear unit with reference to the first fixing unit and the second fixing unit in order to maintain consistent intervals between the plurality of shaft members (130,140,150,160,170,180); and wherein each of the coupler members (330,340,350,360,370) and the gear unit is mounted on the shaft members (130,140,150,160,170,180) passing through them.