The present invention relates to a pin holder structure of an input/output plug for a vehicle phone or Personal Digital Assistant(PDA), and more particularly to an improvement of combination between a pin holder of an input/output plug and a cover plate. The present invention has advantages that because a pin holder is at its upper and lower portions combined with the cover plate which has the corresponding size and shape, it can be prevented from the damage and abrasion due to an outside impact and the cover plate and the circuit board thereon can be prevented from the distortion due to an outside impact and a bad contact between the pin and the circuit board can be prevented because the lower plate of the cover plate is projectedly formed at its bottom portion with a convex portion to have a certain tension.