A living body measuring instrument having a sub-mount on which plural light-emitting devices oscillating at different wavelengths are mounted in proximity, one optical output monitoring device that detects the optical outputs of these light-emitting devices and a light source mounted on the same heat sink which are housed in one can-package, a light-receiving device that detects a signal from a living body, and a circuit that separates the optical output signals from the light-emitting devices, wherein at least one light-emitting device has a light-emitting layer including a In1-xGaxAsyP1-y quantum well layer and a barrier layer on a GaAs substrate, the strain E satisfies 0.4%≦ε≦1.4%, wherein y in the composition satisfies 0.10≦y≦0.45, and the wavelength of the emitted light is from 700 nm to 760 nm.