PURPOSE: To prevent car theft by a method wherein a key cylinder is hardly removed from a garnish even though the garnish is made of synthetic resin and the key cylinder is treated rough for forcible unlocking with a tool like a screwdriver inserted therein, and the strength of fixation for the key cylinder to the garnish is heightened.

CONSTITUTION: In a securing structure wherein a key cylinder 3 is fixed to a synthetic resin granish 2 provided to the outside of a backdoor 11, a reinforcement composed of a fixation wall 41 for the key sylinder 3 and a pair of flanges 42 and 43 formed by bending on both ends of the fixation wall 41 for fitting between a pair of ribs 24 and 29 formed to the inside of the granich 2 is formed. Then, the fixation wall is fixed together with the key cylinder 3 to the inner surface of the granish 2.