A ferrule block comprises a ferrule block body which is attached to an optical device module, which houses in its package an optical device for sending or receiving a light signal, to optically couple to an optical fiber communicating between the optical device module and an external optical communication system and a shell made of an insulating material which is provided at the tip of the ferrule block body, wherein a flange which hits against the tip of the ferrule block body is provided on the outer periphery of the shell.