To provide an electric junction box which can reduce the occurrence of defective assembled products.

On a bottom plate section 24 of a lower J/B case 13 constituting an electric junction box 10, guide walls 28-31 are formed in projecting states. The walls 30 and 31 are integrally formed with the bottom plate section 24, in such a way that the walls 30 and 31 are substantially connected to the intermediate position of the section 24 with a connecting plate 33. On one external side face of an ECU upper case 42 constituting an ECU 40 and having right and left external side faces, two bar-like projections 42a are provided. Then the integrated ECU 40 is inserted into external electric housing section 25 of a main J/B body 11 of the junction box 10 along the guide walls 28-31, so that the projections 42a are positioned between the guide walls 28 and 29. When the ECU 40 is inserted into the housing section 25, the ECU 40 is assembled with the main body 11, so that a group of tab terminals 22 which passed through through-holes 26 are inserted from through-holes 44 and 43a and a connector housing 48.