This super-additive quantum coding gain is, in the simplest saying, such that transmissible information can increase even more than twice when the amount of transmission resources such as the signal power or the bandwidth is doubled for fixed noise characteristics of a channel. According to conventional communication theory, on the other hand, the amount of transmissible information can be increased twice at most. This quantum gain can be particularly remarkable for the signals at the quantum level conveyed by photons and electrons. We have demonstrated a proof-of-principle experiment of the super-additive quantum coding gain by using the ternary symmetric states of a single photon. We prepare the ternary symmetric signals by modulating polarization and spatial paths of a photon, and decode them at the receiver forming quantum entanglement between the degrees of freedom of polarization and spatial paths. We have then confirmed that the amount of information can be extracted more than double the amount that can be obtained when only one of those, the polarization signal or the spatial mode signal, is used for transmission. Our result is related to a new principle that beats the conventional technological limits toward large capacity communications and weak signal detections.