A foldable keyboard includes first, second, and third keyboard units U1, U2, and U3 which are rotatably connected with one another by means of main links (4) and (5) disposed on side end surfaces of each unit. The first and second units U1 and U2 are rotatably connected by means of an auxiliary link (6) parallel to the main link (4), and the second and third units U2 and U3 are rotatably connected by means of an auxiliary link (7) parallel to the main link (4). The first unit U1 is formed with recesses (38) at four corners of a peripheral wall member (12) and the second unit U2 is formed with projections (36) at four corners of an undersurface of the second unit U2 so that the projections (36) are received in the recesses (38) when the first, second, and third units U1, U2, and U3 are disposed (stacked) one upon another into a folded state.