Abstract: Provided are a radioactive contamination monitoring device and a radioactive contamination monitoring method for enabling easy detection of radiation from an object to be monitored in a little surrounding space. The radioactive contamination monitoring device comprises a radiation detection unit, a photoelectric conversion unit for converting the light generated in the radiation detection unit to electricity, and a signal processing unit connected to the photoelectric conversion unit. The radiation detection unit includes a quadrangular prism-shaped light guide bar having a rectangular cross-section and a scintillator attached only to two adjacent side faces of the four side faces of the light guide bar.