A laser diode epitaxial wafer has an n-type GaAs substrate, an n-type cladding layer formed on the n-type GaAs substrate, an active layer formed on the n-type cladding layer, and a p-type cladding layer formed on the active layer. The n-type cladding layer, the active layer, and the p-type cladding layer are formed of an AlGaInP-based material. The p-type cladding layer has carbon as a p-type impurity. The p-type cladding layer has a carrier concentration in the range of not less than 8.0×1017 cm−3 and not more than 1.5×1018 cm−3.