We fabricated a laser diode (LD) exhibiting a lasing from strained GaInAs quantum wells (QWs) embedded in Er,O-codoped GaAs (GaAs:Er,O) by organometallic vapor phase epitaxy (OMVPE). The lasing wavelength was designed to tune to the energy separation between the second excited states 4I11/2 and the ground state 4I15/2 of Er3+ ions. The threshold current for the lasing at room temperature was six times larger than that of a GaInAs QW-LD without Er doping, reflecting ultrafast carrier capture by an Er-related trap in GaAs:Er,O. The Er intensity revealed initially steep increase with injected current density in the region for spontaneous emission from the GaInAs QWs. In the stimulated QW emission region, the intensity continued to increase with the current density.