A cost-effective FBG (Fiber Bragg Grating) interrogation system that includes a tunable laser diode, 6 photodiodes, and several fiber-optic couplers has been developed with very simple coniguration. Especially, it is not necessary to compensate the accurate wavelength because the wavelength sweeping is precisely performed in terms of the response time of which external cavity material is 5 msec. Moreover, time-varying temperature trends as well as spectra of FBGs can be observed through the front display.