An electrical junction box has a fitting member for securing the junction box to a vehicle body. The fitting member has a breakdown accelerating portion for enhancing breakdown of the fitting member when the junction box is pulled to remove it from the vehicle body. The breakdown accelerating portion is positioned in a base side of the fitting piece. By a transverse force caused by pulling an associated wiring harness, the breakdown accelerating portion initiates breakdown of a bracket to separate the junction box from the bracket. Another fitting device has a fitting member formed on a junction box for securing the junction box to a vehicle body. The fitting member has a slot for enhancing breakdown of the fitting member when the junction box is pulled to remove the junction box from the vehicle body, and the fitting member has a compensating piece removably inserted into the slot for adjusting the breakdown of the fitting member.