PURPOSE: To prevent carrier recombination on the surface of a sample by simple constitution, and to enable measurement in a short time without contamination, etc., by measuring the lifetime of a semiconductor through a photoconductive attenuation method under the state in which an electric field is applied and carriers are driven out to the end section of a sample semiconductor.

CONSTITUTION: An electric field is given by lower and upper electrode plates 11, 12 driven by a DC power 13, excess carriers are driven out to the end section of an Si wafer as a sample, and recombination on the surface of the wafer 9 is prevented. Consequently, pretreatment in which the wafer is thermally oxidized and an oxide film is attached is unnecessitated, and the electric field is applied and the lifetime of the wafer 9 is measured through a photoconductive attenuation method through pulse-beam application by an irradiation light source 2, a reflecting plate 8, a circulator 5, a crystal detector 6, etc. Carrier recombination is prevented without requiring pretreatment according to simple constitution in which the electrode plates for generating the electric field is mounted, thus measuring the lifetime in a short time without contamination, etc., by pretreatment.