Provided is a detecting element that detects a parameter for a predetermined gas or liquid in a surrounding atmosphere by being excited by excitation light and generating light corresponding to the surrounding atmosphere, the detecting element including: a substrate; and nanoscale crystal structures formed on the substrate and constituted by a compound semiconductor light emitting element having a heterostructure well layer, wherein when the nanoscale crystal structures adsorb atoms or molecules of the predetermined gas or liquid, there is distortion of a band of a structure with a smaller bandgap width in the well layer, this distortion brings about a change in transition energy, and this change brings about a change in at least one of an intensity and a wavelength of light generated by the well layer, thereby indicating the parameter for the gas or the liquid.