A new reactor, named APSIS for Atmospheric Photochemistry SImulated by Synchrotron, is designed for simulating the reactivity occurring in planetary upper atmospheres. In this reactor, a gas mixture roughly reproducing the main Titan's atmosphere composition (N2/CH4 = 90/10) is irradiated by a continuous-spectrum in the 60−350 nm range, provided by the DISCO beamline at SOLEIL synchrotron radiation facility. This spectral range enables the dissociation and ionization of N2 and CH4, as observed in plasma reactors and Titan's ionosphere. The neutral products are detected in situ by quadrupole mass spectrometry, and collected with a cryogenic trap for ex-situ analysis by gas chromatography-mass spectrometry. The detected reaction products include C2, C3, C4 and probably C5 organic compounds, with important amounts of nitrogen-bearing species: HCN, CH3CN and C2N2. Neutral mass spectra obtained with APSIS are compared with INMS experiments of the Cassini space probe in the upper Titan atmosphere and with other results of current Titan atmosphere chemistry laboratory simulations.