The second chapter describes the experimental setup of gas-phase anion photoelectron spectroscopy. The composition of the apparatus is overviewed in the first section. Details of each component (an electrospray ionization source, a quadrupole linear ion trap, a time-of-flight mass spectrometer, and a magnetic-bottle photoelectron spectrometer) are described in the following sections. Especially, the quadrupole linear ion trap I designed and implemented is described in detail.