To provide a precast base 10 and a step which are excellent in joint strength and which does not require an extra construction period.

A precast base 10 is composed of precast base blocks planted on a base 1 and connected together. The straight line-like precest concrete blocks 2 are made into contact with and connected with at their side faces L-like precast concrete blocks 3A, 3B, 3D 3E having connecting parts 3a, 3b, 3c, 3d having end parts bent at a right angle, through the intermediary of the connecting parts 3a, 3b, 3c, 3d.