We developed a combined probe microscope—a scanning probe near-field optical microscope (SNOM) combined with Kelvin probe force microscope (KFM) that uses a slim and bent optical fiber probe (S/B fiber probe). The developed SNOM-KFM system enables near-field photoexcitation through an apex of the S/B fiber probe during KFM measurement, so that the photoexcitation effects on surface potential (SP) can be measured with submicron spatial resolution. By measuring the SP of tris(8-hydroxyquinolinato) aluminum(III) (Alq3) thin films, we found that the S/B fiber probes have large negative values in the KFM transfer function. Near-field photoexcitation was performed on Alq3 thin films through the S/B fiber probes, and the spatial pattern of photoinduced reduction in SP was visualized by KFM measurement with the same probe.