A three-dimensional simulation was conducted with a cloud-resolving model to investigate mesoscale gravity waves generated by cumulus convection that propagate to the mesospheric and lower thermospheric (MLT) region. It is found that both individual convective turrets and mesoscale convective systems excite gravity waves, resulting in a broad scale distribution. Waves excited by the former have conically shaped phase surfaces as previously reported and are conspicuous up to around the stratopause. Waves excited by the latter dominate in the MLT region. Frequent wave breaking is found above 85 km, where convective instability is found typically in the initial stage, leading to unstable shear with billows resembling the ripple-type structures observed frequently in airglow imaging.