An object is to provide, in place of a cube toy such as Yoshimoto Cube, a wide variety of playing patterns, playing patterns which cannot be predicted in terms of change in forms, a polyhedral toy which can be enjoyed in terms of change in form even when only one polyhedral toy is used, and a polyhedral toy having extensibility for achieving a wide variety of contents of play through combination of two or more polyhedral toys. Therefore, when a polyhedral piece (U1) forming the toy is formed with three quadrangular pyramids (G1 to G3) having, among six triangular faces (T1 to T6) of a cube (R), three faces (R1 to R3) as bottom faces, the polyhedral piece (U1) includes a triangle surface (10) formed of six triangular faces (T1 to T6) other than respective side faces of the quadrangular pyramids (G1 to G3) placed on one another. When polyhedral pieces (U1 to U8) each having the configuration described above form a toy (1) unfolded into a cuboid shape of two rows and four columns as illustrated in FIG. 1, in plan view on a top face of the toy (1), in each of the first row and the second row, the triangle surface (10), the third face (R3), the third face (R3), and the triangle surface (10) are arranged in the stated order.