A lead frame for use in an optical semiconductor device has a die pad portion on which an optical semiconductor element is mounted and a lead portion electrically connectable with the optical semiconductor element. A surface on a lead frame substrate forming a part of or an entirety of the die pad portion and the lead portion is laminated with a glossy Ni plating layer having a gloss of 2.0-3.5 and a noble metal plating layer including an Ag plating layer, as an uppermost layer, having a gloss of 1.6 or more.