Abstract: An electrical connection box is provided that is capable of positively preventing improper connections. A mounting area is formed on a side wall of an electrical connection box. On the mounting area, a generally U-shaped bolt housing recess is provided. At the deepest area, or closed end, of the bolt housing recess, a bolt is inserted, extends through a washer, and is fastened with a nut. An upwardly extending protrusion is formed at the open end of the bolt housing recess on the mounting area. The protrusion is so formed that, in tightening the bolt and nut at the deepest area, or closed end, of the bolt housing recess, the protrusion does not interfere with the washer. In addition, the height of the protrusion is set in such a manner that it is higher than a protruding height of the bolt in a condition in which the bolt is inserted in the bolt housing recess.