PURPOSE: To fit a fitted body to a fitting portion surely by putting lock pins into lock holes easily under pressure by forming the lock pins deformably in the pitch direction of the lock holes.

CONSTITUTION: A pair of lock pins 25, 27 are projectingly provided from the upper surface 3a of the box main body 3 of an electric connection box 1. The lock pins 25, 27 possess eight flexible outer wall post bodies 31 provided projectingly from the upper surface of the box main body 3 with slits 29 interposed. A pitch L2 between lock holes 21, 23 is arranged shorter in regard to a pitch L1 between the lock pins 25, 27, and the insertion tip portions 33, 33 of the lock pins 25, 27 are inserted into the lock holes, 21, 23 and the lock pins 25, 27 are put into the lock holes 21, 23 under pressure by pressing the box main body 3 against a beacket 15 side. At this time, the lock pins 25, 27 are put into the lock holes 21, 23 under pressure while deforming themselves in a direction approaching mutually. The lock pins 25, 27 are inserted into the lock holes 21, 23 while their diameters are being reduced. Accordingly, it can be accomplished that the lock pins 25, 27 are easily put into the lock holes 21, 23 under pressure and fitted to the bracket 15.