To provide a hydraulic control device capable of preventing three kinds of spool valves from being incorrectly assembled.

In the three kinds of spool valves α, "a diameter difference of O-ring mounting parts A, B, and C different in each of three kinds of spool valves α" and "an insertion difference of two insertion lengths L1 and L2 against a regulation difference 10" are provided. By this, it becomes possible to prevent the spool valve α from coinciding with an insertion hole β when a different kind of the spool valve α is assembled incorrectly to the insertion hole β of a valve body 1. As a result, when the spool valve α is assembled incorrectly, the spool valve α does not coincide with the insertion hole β, and it is possible to securely prevent the three kinds of spool valves α from being incorrectly assembled.