To provide an estimated dampening water dilution device which can produce dampening water to be used by an offset printer at a rate of highly precise dilution.

This estimated dampening water dilution device makes a production and a supply of dampening water to be used by the offset printer and operates as follows: when an overall control means detects with the help of a liquid level sensor the fact that the liquid level of the dampening water inside a dampening water producing tank, is lower compared with a predetermined value, a stock solution of the dampening water is supplied to a dampening water stock solution measuring container by a stock solution pump and a predetermined amount of a stock solution of the dampening water is once stored in the dampening water stock solution measuring container. After that, the dampening water stock solution is supplied to a dampening water producing tank after opening a discharge port, and the dampening water stock solution, sticking to the interior of the dampening water stock solution measuring container, is discharged from the discharge port while washing out the dampening water stock solution by supplying water with the help of a water supply means. Further, water is supplied to the dampening water producing tank until the liquid level of the dampening water measured using the liquid level sensor indicates the specified value.