An assembly toy having a first toy block and a second toy block linkable to each other, wherein each of the toy blocks includes: a block portion; a first flat surfaces and a second flat surface that are formed at both ends of the block portion; at least two columnar projecting parts (11a, 11b, 11c, 11d) that project and extend vertically from each of the flat surfaces (75a, 75b); and at least two arc-shaped strip-like depressed parts (12a, 12b, 12c, 12d) that are formed so as to be vertically indented from each of the flat surfaces (75a, 75b) in a direction opposite to a projection direction of the projecting parts (11a, 11b, 11c, 11d), the projecting parts (11a, 11b, 11c, 11d) and the depressed parts (12a, 12b, 12c, 12d) are provided on the same inner circumference and are alternately disposed on the flat surface, the projecting parts (11a, 11b, 11c, 11d) are detachably fittable into the depressed parts (12a, 12b, 12c, 12d) in a width direction of each of the depressed parts (12a, 12b, 12c, 12d), and the projecting parts (11a, 11b, 11c, 11d) of the first toy block and the second toy block move in an arc-shaped pattern along the depressed parts (12a, 12b, 12c, 12d) of the first toy block and the second toy block, while a state in which the first toy block and the second toy block are linked together is maintained, to allow the first toy block to rotate relative to the second toy block, characterized in that the block portion has a circular-shaped section which has a uniform diameter from one of both ends to the other end and which forms a cylindrical part, the outer circumference of the two flat surfaces (75a, 75b) that are formed at both ends of the block portion each have a circular shape of the same diameter, and the inner circumference has a same diameter in each of the flat surfaces (75a, 75b), wherein another cylindrical part is provided, wherein the another cylindrical part is combined at right angles with the cylindrical part such that a part of the another cylindrical part is buried in the center of the cylindrical part, wherein a third flat surface is formed at an end of the another cylindrical part such that it is disposed in a direction which is perpendicular to a direction in which the first flat surfaces or the second flat surface is disposed, wherein the third flat surface has at least two columnar projecting parts and at least two arc-shaped strip-like depressed parts having the same structures as those of the at least two columnar projecting parts (11a, 11b, 11c, 11d) and the at least two arc-shaped strip-like depressed parts (12a, 12b, 12c, 12d) on the first flat surface or on the second flat surfaces. a block portion; a first flat surfaces and a second flat surface that are formed at both ends of the block portion; at least two columnar projecting parts (11a, 11b, 11c, 11d) that project and extend vertically from each of the flat surfaces (75a, 75b); and at least two arc-shaped strip-like depressed parts (12a, 12b, 12c, 12d) that are formed so as to be vertically indented from each of the flat surfaces (75a, 75b) in a direction opposite to a projection direction of the projecting parts (11a, 11b, 11c, 11d), the projecting parts (11a, 11b, 11c, 11d) and the depressed parts (12a, 12b, 12c, 12d) are provided on the same inner circumference and are alternately disposed on the flat surface, the projecting parts (11a, 11b, 11c, 11d) are detachably fittable into the depressed parts (12a, 12b, 12c, 12d) in a width direction of each of the depressed parts (12a, 12b, 12c, 12d), and the projecting parts (11a, 11b, 11c, 11d) of the first toy block and the second toy block move in an arc-shaped pattern along the depressed parts (12a, 12b, 12c, 12d) of the first toy block and the second toy block, while a state in which the first toy block and the second toy block are linked together is maintained, to allow the first toy block to rotate relative to the second toy block, characterized in that the block portion has a circular-shaped section which has a uniform diameter from one of both ends to the other end and which forms a cylindrical part, the outer circumference of the two flat surfaces (75a, 75b) that are formed at both ends of the block portion each have a circular shape of the same diameter, and the inner circumference has a same diameter in each of the flat surfaces (75a, 75b), wherein another cylindrical part is provided, wherein the another cylindrical part is combined at right angles with the cylindrical part such that a part of the another cylindrical part is buried in the center of the cylindrical part, wherein a third flat surface is formed at an end of the another cylindrical part such that it is disposed in a direction which is perpendicular to a direction in which the first flat surfaces or the second flat surface is disposed, wherein the third flat surface has at least two columnar projecting parts and at least two arc-shaped strip-like depressed parts having the same structures as those of the at least two columnar projecting parts (11a, 11b, 11c, 11d) and the at least two arc-shaped strip-like depressed parts (12a, 12b, 12c, 12d) on the first flat surface or on the second flat surfaces.