A portable keyboard, comprising: a plurality of key assemblies including a plurality of key tops; a main body having a pillar shape defined by a number (n) of sides, which is located in the vicinity of a first key assembly among a plurality of the key assemblies; wherein the number (n) is equal to or greater than 5 and wherein a plurality of the sides of the main body have a same size; a flexible connection member configured to connect the plurality of key assemblies with the main body; and a main board configured to be embedded in the inside of the main body and process input signals inputted from the plurality of key assemblies, wherein the main body comprises: a first side having one edge connected with the flexible connection member, a second side adjacent to another edge of the first side and the second side of which an angle with the first side is greater than 90 degrees, and a cradle configured to be pivotably coupled to the second side using a hinge at one end, wherein the cradle has a first surface in contact with the second side of the main body when the hinge is closed, wherein the cradle further comprises a mounting groove which is formed at an upper side of the cradle, wherein the upper side of the cradle is the side opposite to the side of the cradle which contacts the floor when the first side of the main body is mounted on a floor, and wherein the mounting groove is elongated from the upper side of the cradle towards the side of the cradle which contacts the floor; characterized in that: the elongation of the mounting groove is slanted towards the hinge such that a lower part of the mounting groove is closer to the hinge than the upper part of the mounting groove, wherein the upper part of the mounting groove is at the upper side of the cradle; and a rib protrudes from an outskirt of the mounting groove in such a manner that the rib protrudes from the first surface of the cradle towards the second side of the main body when the hinge is closed, wherein a width of the mounting groove is wider at the lower part of the mounting groove than at the upper part of the mounting groove. a plurality of key assemblies including a plurality of key tops; a main body having a pillar shape defined by a number (n) of sides, which is located in the vicinity of a first key assembly among a plurality of the key assemblies; wherein the number (n) is equal to or greater than 5 and wherein a plurality of the sides of the main body have a same size; a flexible connection member configured to connect the plurality of key assemblies with the main body; and a main board configured to be embedded in the inside of the main body and process input signals inputted from the plurality of key assemblies, wherein the main body comprises: a first side having one edge connected with the flexible connection member, a second side adjacent to another edge of the first side and the second side of which an angle with the first side is greater than 90 degrees, and a cradle configured to be pivotably coupled to the second side using a hinge at one end, a first side having one edge connected with the flexible connection member, a second side adjacent to another edge of the first side and the second side of which an angle with the first side is greater than 90 degrees, and a cradle configured to be pivotably coupled to the second side using a hinge at one end, wherein the cradle has a first surface in contact with the second side of the main body when the hinge is closed, wherein the cradle further comprises a mounting groove which is formed at an upper side of the cradle, wherein the upper side of the cradle is the side opposite to the side of the cradle which contacts the floor when the first side of the main body is mounted on a floor, and wherein the mounting groove is elongated from the upper side of the cradle towards the side of the cradle which contacts the floor; characterized in that: the elongation of the mounting groove is slanted towards the hinge such that a lower part of the mounting groove is closer to the hinge than the upper part of the mounting groove, wherein the upper part of the mounting groove is at the upper side of the cradle; and a rib protrudes from an outskirt of the mounting groove in such a manner that the rib protrudes from the first surface of the cradle towards the second side of the main body when the hinge is closed, wherein a width of the mounting groove is wider at the lower part of the mounting groove than at the upper part of the mounting groove. the elongation of the mounting groove is slanted towards the hinge such that a lower part of the mounting groove is closer to the hinge than the upper part of the mounting groove, wherein the upper part of the mounting groove is at the upper side of the cradle; and a rib protrudes from an outskirt of the mounting groove in such a manner that the rib protrudes from the first surface of the cradle towards the second side of the main body when the hinge is closed, wherein a width of the mounting groove is wider at the lower part of the mounting groove than at the upper part of the mounting groove.