A radiation detector comprises an energy/electricity converter having a detection area for detecting incident radiation, and electrodes connecting the converter to an external driving circuit for driving the converter to convert energy of the incident radiation detected by the detection area of the converter into an electric signal. A collimator is integrally connected to the converter and has an opening for transmitting radiation to irradiate the detection area of the converter and portions for preventing radiation from irradiating a part of the converter other than the detection area. A spacer is integrally connected to the collimator and the converter for maintaining a preselected distance between the collimator and the detection area of the converter.