A keyboard apparatus comprising: a key unit (UNT, UNT2, UNT3, WU1, WU2, WU11, WU12, BU11, BU12) having a plurality of key main bodies (27, 28) each of which is adapted to be supported for pivotal motion in a key depression/release direction by a common base end (21, 22, 23, 220, 221, 222, 223) via a corresponding one of thin plate-like hinges (24, 25, 26); and a key frame (10, 110, 210, 300) having a base end support adapted to fixedly support the common base end (21, 22, 23, 220, 221, 222, 223) of said key unit (UNT, WU, BU, UNT2, UNT3, WU1, WU2, WU11, WU12, BU11, BU12), wherein the hinges (24, 25, 26) of said key unit (UNT, WU, BU, UNT2, UNT3, WU1, WU2, WU11, WU12, BU11, BU12) are formed at respective rear ends of the plurality of key main bodies (27, 28) to extend in a direction to cross the key depression surfaces (27a, 28a) of the key main bodies (27, 28) and parallel to a key arrangement direction, wherein the common base end (21, 22, 23, 220, 221, 222, 223) is fitted and fixed to the base end support using elastic deformation, in a front end-to-rear end direction of the plurality of key main bodies (27, 28), of an elastic member (16, 17) included in at least one of the common base end (21, 22, 23, 220, 221, 222, 223) of said key unit (UNT, WU, BU, UNT2, UNT3, WU1, WU2, WU11, WU12, BU11, BU12) and the base end support of said key frame (10, 110, 210, 300), one of the common base end (21, 22, 23, 220, 221, 222, 223) and the base end support is formed with a U-shaped recessed groove (15, 115, 215, 61c, 62c) opening upward or downward and extending in the key arrangement direction, and the other of the common base end (15, 115, 215, 61c, 62c) and the base end support is formed with a ridge-like protrusion extending in the key arrangement direction and adapted to be fitted to the U-shaped recessed groove (15, 115, 215, 61c, 62c), and at the position where the elastic member is situated in the common base end or the base end support, one of the common base end (21, 22, 23, 220, 221, 222, 223) and the base end support is formed with protrusions, and the other of the common base end (21, 22, 23, 220, 221, 222, 223) and the base end support is formed with fitting holes (16c, 21b, 221a) adapted to be fitted with the protrusions when the common base end (21, 22, 23, 220, 221, 222, 223) is fitted and fixed to the base end support, whereby a position of the common base end (21, 22, 23, 220, 221, 222, 223) relative to the base end support in the key arrangement direction and in a vertical direction is restricted when the protrusions are fitted to the fitting holes. a key unit (UNT, UNT2, UNT3, WU1, WU2, WU11, WU12, BU11, BU12) having a plurality of key main bodies (27, 28) each of which is adapted to be supported for pivotal motion in a key depression/release direction by a common base end (21, 22, 23, 220, 221, 222, 223) via a corresponding one of thin plate-like hinges (24, 25, 26); and a key frame (10, 110, 210, 300) having a base end support adapted to fixedly support the common base end (21, 22, 23, 220, 221, 222, 223) of said key unit (UNT, WU, BU, UNT2, UNT3, WU1, WU2, WU11, WU12, BU11, BU12), wherein the hinges (24, 25, 26) of said key unit (UNT, WU, BU, UNT2, UNT3, WU1, WU2, WU11, WU12, BU11, BU12) are formed at respective rear ends of the plurality of key main bodies (27, 28) to extend in a direction to cross the key depression surfaces (27a, 28a) of the key main bodies (27, 28) and parallel to a key arrangement direction, wherein the common base end (21, 22, 23, 220, 221, 222, 223) is fitted and fixed to the base end support using elastic deformation, in a front end-to-rear end direction of the plurality of key main bodies (27, 28), of an elastic member (16, 17) included in at least one of the common base end (21, 22, 23, 220, 221, 222, 223) of said key unit (UNT, WU, BU, UNT2, UNT3, WU1, WU2, WU11, WU12, BU11, BU12) and the base end support of said key frame (10, 110, 210, 300), one of the common base end (21, 22, 23, 220, 221, 222, 223) and the base end support is formed with a U-shaped recessed groove (15, 115, 215, 61c, 62c) opening upward or downward and extending in the key arrangement direction, and the other of the common base end (15, 115, 215, 61c, 62c) and the base end support is formed with a ridge-like protrusion extending in the key arrangement direction and adapted to be fitted to the U-shaped recessed groove (15, 115, 215, 61c, 62c), and at the position where the elastic member is situated in the common base end or the base end support, one of the common base end (21, 22, 23, 220, 221, 222, 223) and the base end support is formed with protrusions, and the other of the common base end (21, 22, 23, 220, 221, 222, 223) and the base end support is formed with fitting holes (16c, 21b, 221a) adapted to be fitted with the protrusions when the common base end (21, 22, 23, 220, 221, 222, 223) is fitted and fixed to the base end support, whereby a position of the common base end (21, 22, 23, 220, 221, 222, 223) relative to the base end support in the key arrangement direction and in a vertical direction is restricted when the protrusions are fitted to the fitting holes.