An inspection device , comprising: a THz wave irradiation unit for irradiating a specimen with THz waves which are oscillated by a THz wave oscillator ; a THz wave sensing unit for detecting transmitted waves or reflected waves of the THz waves emitted to the specimen ; and an information processing unit for acquiring an intensity distribution of the transmitted waves or the reflected waves of the specimen from intensity data of the transmitted waves or the reflected waves of the specimen irradiated with the THz waves, characterized in that the THz wave irradiation unit comprises: the THz wave oscillator ; a scanning device irradiated with THz waves oscillated by the THz wave oscillator ; and a first light-collecting optical component inserted between the scanning device and the specimen , wherein the inspection device is configured to emit the THz waves to the specimen via the first light- collecting optical component at an angle of incidence set from 10 to 50 degrees with respect to the thickness direction of the specimen not to cause interference between the reflected waves and incident waves, the information processing unit is configured to acquire 2-dimensional intensity distribution of the transmitted waves or the reflected waves , and to detect whether a foreign matter is adhering to the specimen at the time of inspection is detected by comparing the intensity distribution obtained when the specimen without attachment of the foreign matter is detected and the intensity distribution obtained when the specimen is detected at the time of inspection. a THz wave irradiation unit for irradiating a specimen with THz waves which are oscillated by a THz wave oscillator ; a THz wave sensing unit for detecting transmitted waves or reflected waves of the THz waves emitted to the specimen ; and an information processing unit for acquiring an intensity distribution of the transmitted waves or the reflected waves of the specimen from intensity data of the transmitted waves or the reflected waves of the specimen irradiated with the THz waves, characterized in that the THz wave irradiation unit comprises: the THz wave oscillator ; a scanning device irradiated with THz waves oscillated by the THz wave oscillator ; and a first light-collecting optical component inserted between the scanning device and the specimen , the THz wave oscillator ; a scanning device irradiated with THz waves oscillated by the THz wave oscillator ; and a first light-collecting optical component inserted between the scanning device and the specimen , wherein the inspection device is configured to emit the THz waves to the specimen via the first light- collecting optical component at an angle of incidence set from 10 to 50 degrees with respect to the thickness direction of the specimen not to cause interference between the reflected waves and incident waves, the information processing unit is configured to acquire 2-dimensional intensity distribution of the transmitted waves or the reflected waves , and to detect whether a foreign matter is adhering to the specimen at the time of inspection is detected by comparing the intensity distribution obtained when the specimen without attachment of the foreign matter is detected and the intensity distribution obtained when the specimen is detected at the time of inspection. <EOS>