To hold workability in a place such as a mountainous region where an admission passage is narrow and a large-scale heavy machine or vehicle is difficult to enter.

In a method for producing a fish-way block 10 splittable through split surfaces, a pair of connection plates 13 are arranged at the positions along the split surfaces 12 within a manufacturing form as partition plates in a mutual close contact state prior to work casting concrete into the manufacturing form of the fish-way block 10 and, after concrete cast into the manufacturing form so as to embed the partition plates is cured and demolded, the close contact state of a pair of the connection plates 13 is released to constitute the fish-way block 10 in a manner possible to split. The fish-way block 10 thus produced is split to be reduced in its wt. to become easily susceptible to transport work or assembling work and, when the split blocks are again integrated, a pair of the connection plates 13 form accurate close contact surfaces to the split surfaces to easily integrate the split blocks in a close contact state.