A portable keyboard comprising: a polygonal pillar-shaped main body having a recessed part ; a key assembly that is formed adjacent to the polygonal pillar-shaped main body and includes a plurality of key arrangements (121, 122, 123, 124, and 125) each having multiple keys formed in a first direction, the key arrangements (121, 122, 123, 124, and 125) formed in a second direction intersecting the first direction, so that the key arrangements (121, 122, 123, 124, and 125) cover each side of the polygonal pillar-shaped main body when rolled up onto the polygonal pillar-shaped main body , wherein a magnet is provided in the key assembly ; a flexible connecting member electrically connecting the key assembly and the polygonal pillar-shaped main body ; a pair of rotary members each including a hinge part fixed at the polygonal pillar-shaped main body and a supporting part extending from a fitting part that extends from the hinge part and has a slot to fit in a mobile terminal , wherein each rotary member is rotatable around the hinge part ; a magnet embedded in both rotary members ; a hall sensor arranged in the polygonal pillar-shaped main body and adapted to detect whether the rotary members are unfolded or whether the key assembly is rolled up; and a controller adapted to control the operation of the key assembly, wherein the controller is configured to turn off the portable keyboard in a first state where the pair of rotary members is disposed in the recessed part or where the key assembly is rolled up around the polygonal pillar-shaped main body and to turn on the portable keyboard in a second state where the pair of rotary members is released from the recessed part or where the key assembly is unrolled from the polygonal pillar-shaped main body . a polygonal pillar-shaped main body having a recessed part ; a key assembly that is formed adjacent to the polygonal pillar-shaped main body and includes a plurality of key arrangements (121, 122, 123, 124, and 125) each having multiple keys formed in a first direction, the key arrangements (121, 122, 123, 124, and 125) formed in a second direction intersecting the first direction, so that the key arrangements (121, 122, 123, 124, and 125) cover each side of the polygonal pillar-shaped main body when rolled up onto the polygonal pillar-shaped main body , wherein a magnet is provided in the key assembly ; a flexible connecting member electrically connecting the key assembly and the polygonal pillar-shaped main body ; a pair of rotary members each including a hinge part fixed at the polygonal pillar-shaped main body and a supporting part extending from a fitting part that extends from the hinge part and has a slot to fit in a mobile terminal , wherein each rotary member is rotatable around the hinge part ; a magnet embedded in both rotary members ; a hall sensor arranged in the polygonal pillar-shaped main body and adapted to detect whether the rotary members are unfolded or whether the key assembly is rolled up; and a controller adapted to control the operation of the key assembly, wherein the controller is configured to turn off the portable keyboard in a first state where the pair of rotary members is disposed in the recessed part or where the key assembly is rolled up around the polygonal pillar-shaped main body and to turn on the portable keyboard in a second state where the pair of rotary members is released from the recessed part or where the key assembly is unrolled from the polygonal pillar-shaped main body . <EOS>