To provide a mounting structure of electrical units on board wherein a sure coupling of mutual connectors and mounting of electrical units can be made by a simple operation.

A male connector 17 is movably installed at a wall part 11B of an instrument panel 11 to a mounting direction (x direction), and a guide groove 13 is formed at a side wall of electrical units housing space 11A. The guide groove 13 is composed of a horizontal guide part 13A and a tilting guide part 13B, and by the fact that a guide protrusion 14 that was protrudingly installed at a side wall of electrical units on board 12 has been guided by the tilting guide part 13B, a female connector 22 installed at a front end part of electrical units 12 on board is fitted into the male connector 17, and accompanied with this, the female connector 22 is made to move forward to the mounting direction. On this account, a sure coupling of connectors each other is made possible by a simple operation.