To provide a unit device which can fit without looseness and remove without damage and can be manufactured at a low price.

When fitting a stay to the upper and the lower cases of a unit device to fix it to a vehicle body, a cap hole 41 having the first walls 43, 44 formed into about the width of two faces of a hexagonal column shaped nut and stopping the rotation of the nut and second walls 45, 46 to cross at right angle with a screwed direction of the nut to face the both sides of the nut are arranged inside the side face of the lower case, and the screw part 56 of the bolt 55 passing through a inserting hole 48 of the second wall 45 from the inserting hole 22 of the stay is screwed into the screw hole of the nut kept and held inside this cap hole.