We report the observation of gamma-ray emission from the supernova remnant G106.3+2.7 in the 100 TeV energy region with the Tibet air shower array combined with the muon detector array. The gamma-ray emission is detected at a significance of 6.1σ above 10 TeV. The centroid of the gamma-ray emission, situated 0.44◦ away from the pulsar PSR J2229+6114 at the north-east corner of G106.3+2.7, is found to be coincident with the location of a molecular cloud. This morphological feature favors a hadronic origin via the π0 decay caused by accelerated relativistic protons regarding the gamma-ray emission mechanism of G106.3+2.7, over a leptonic one via the inverse-Compton scattering by relativistic electrons. The differential gamma-ray energy spectrum can be expressed by a single power law from 6 TeV to 115 TeV as dN/dE = N0(E/40 TeV)−Γ with a flux of N0 = (9.5±1.6)×10−16 [cm−2 s−1 TeV−1] and an index of Γ = 2.95±0.17. In the hadronic scenario, we estimate the cut-off energy of parent cosmic-ray particles (protons) to be around 0.5 PeV.