A detecting apparatus for detecting a fine geometry on a surface of a sample, wherein an irradiation beam is irradiated against the sample placed in a different environment different from an atmosphere and a secondary radiation emanated from the sample is detected by a sensor, and wherein the sensor is disposed at an inside of the different environment, a processing device to process detection signals from the sensor is disposed at an outside of the different environment, and a transmission means transmits detection signals from the sensor to the processing device.