A laser diode device includes a laminated structure in which a first compound semiconductor layer, a third compound semiconductor layer that has a light emitting region and a saturable absorption region, and a second compound semiconductor layer are sequentially layered, a second electrode, and a first electrode. The laminated structure has ridge stripe structure. The second electrode is separated into a first section to obtain forward bias state by applying a direct current to the first electrode through the light emitting region and a second section to add electric field to the saturable absorption region by an isolation trench. When minimum width of the ridge stripe structure is WMIN, and width of the ridge stripe structure of the second section of the second electrode in an interface between the second section of the second electrode and the isolation trench is W2, 1