Recently electronic devices using organic materials have been extensively studied. The elucidation of the electronic structures of the materials and interfaces of such devices is indispensable for understanding and improving devices. Since the properties of organic devices are affected by atmospheric gas effect, the electronic structures not only in vacuum but also in atmospheric condition should be examined. Recently, we have developed an apparatus for measuring photoelectron yield spectroscopy (PYS) for that purpose. Photoelectrons emitted into atmosphere are extracted by an external field and probed as a current with an ammeter. Such current-mode detection is operative in any condition including vacuum and air. In this paper, we report on the details of the apparatus, the application to various organic films and powders. The trial to probe the electronic structures of organic/metal interfaces by PYS is also reported.