A distributed optical fiber sensor comprising an optical fiber as a sensor, and further comprising: a Brillouin measuring unit for measuring a Brillouin frequency shift amount caused by a strain and a temperature generated in the optical fiber by using a Brillouin scattering phenomenon; a Rayleigh measuring unit for measuring a Rayleigh frequency shift amount caused by the strain and temperature generated in the optical fiber by using a Rayleigh scattering phenomenon; and a calculation unit for calculating the strain and temperature generated in the optical fiber based on the Brillouin frequency shift amount measured by the Brillouin measuring unit and the Rayleigh frequency shift amount measured by the Rayleigh measuring unit; wherein the Rayleigh measuring unit is configured to measure the Rayleigh frequency shift amount by determining a frequency sweep range of pulsed light for measuring Rayleigh backscattered light based on the Brillouin frequency shift amount measured by the Brillouin measuring unit, and measuring the Rayleigh backscattered light by sweeping the pulsed light in the determined sweep range, and wherein the Rayleigh measuring unit is configured to set, as a first frequency, a first Rayleigh frequency shift amount calculated based on a variation in temperature when the entire Brillouin frequency shift amount measured by the Brillouin measuring unit is deemed a shift amount caused by the temperature, and to set, as a second frequency, a second Rayleigh frequency shift amount calculated based on a variation in strain when the entire Brillouin frequency shift amount measured by the Brillouin measuring unit is deemed a shift amount caused by the strain, and further configured to determine the sweep range based on the first frequency and the second frequency. a Brillouin measuring unit for measuring a Brillouin frequency shift amount caused by a strain and a temperature generated in the optical fiber by using a Brillouin scattering phenomenon; a Rayleigh measuring unit for measuring a Rayleigh frequency shift amount caused by the strain and temperature generated in the optical fiber by using a Rayleigh scattering phenomenon; and a calculation unit for calculating the strain and temperature generated in the optical fiber based on the Brillouin frequency shift amount measured by the Brillouin measuring unit and the Rayleigh frequency shift amount measured by the Rayleigh measuring unit; wherein the Rayleigh measuring unit is configured to measure the Rayleigh frequency shift amount by determining a frequency sweep range of pulsed light for measuring Rayleigh backscattered light based on the Brillouin frequency shift amount measured by the Brillouin measuring unit, and measuring the Rayleigh backscattered light by sweeping the pulsed light in the determined sweep range, and wherein the Rayleigh measuring unit is configured to set, as a first frequency, a first Rayleigh frequency shift amount calculated based on a variation in temperature when the entire Brillouin frequency shift amount measured by the Brillouin measuring unit is deemed a shift amount caused by the temperature, and to set, as a second frequency, a second Rayleigh frequency shift amount calculated based on a variation in strain when the entire Brillouin frequency shift amount measured by the Brillouin measuring unit is deemed a shift amount caused by the strain, and further configured to determine the sweep range based on the first frequency and the second frequency.