An optical fiber holder 21 includes an alignment mechanism part 51 having a base part 52 formed in a holder body 22, a movable base part 53 arranged on the base part 52, and an alignment lid 54 arranged on the movable base part 53. A slit 61 capable of receiving parallel-arranged plural optical fiber core wires 11 is formed between the movable base part 53 and the alignment lid 54 in the superposed state. By turning the movable base part 53 and the alignment lid 54 to the side of the base part 52, the optical fiber core wires 11 received in the slit 61 are aligned in a receiving groove 23 formed in the holder body 22.