We report the confirmation of a TESS-discovered transiting super-Earth planet orbiting a mid-G star, HD307842 (TOI-784). The planet has a period of 2.8days, and the radial velocity (RV) measurements constrain the mass to be 9.67_-0.82_^+0.83^M{Earth}. We also report the discovery of an additional planet candidate on an outer orbit that is most likely nontransiting. The possible periods of the planet candidate are approximately 20^-63^days, with the corresponding RV semiamplitudes expected to range from 3.2 to 5.4m/s and minimum masses from 12.6 to 31.1 M{Earth}. The radius of the transiting planet (planet b) is 1.93_-0.09_^+0.11^R{Earth}, which results in a mean density of 7.4_-1.2_^+1.4^g/cm^3^ suggesting that TOI-784b is likely to be a rocky planet though it has a comparable radius to a sub-Neptune. We found TOI-784 b is located at the lower edge of the so-called "radius valley" in the radius versus insolation plane, which is consistent with the photoevaporation or core-powered mass-loss prediction. The TESS data did not reveal any significant transit signal of the planet candidate, and our analysis shows that the orbital inclinations of planet b and the planet candidate are 88.60deg_-0.86_^+0.84^ and <~88deg^3^-89deg^2^, respectively. More RV observations are needed to determine the period and mass of the second object, and search for additional planets in this system.