A detection unit for use in an optical coherence tomography system for analyzing an object (EY, R) to be measured using polarization, the detection unit being adapted to detect, on a different polarization component basis, interference polarization beam which is obtained by causing a reference polarization beam, which is used as reference light when generating a tomographic image and which is generated based on a predetermined polarization beam, and an object-reflected polarization beam, which is reflected from the object to be measured based on an irradiation of the object to be measured with the predetermined polarization beam, to interfere with each other, comprising: a diffraction grating adapted to separate the received interference polarization beam on a wavelength basis; a polarization optical element that has a birefringence characteristic including a first refractive index and a second refractive index, a lens that causes the interference polarization beams separated on a wavelength basis to be arranged in order of wavelengths from the first end to the second end of the entrance face of the polarization optical element, and causes such beams to enter the polarization optical element and a detection section; the polarization optical element being adapted to receive the separated interference polarization beams of the respective wavelengths in a wavelength order and in a parallel manner, to separate the separated interference polarization beam of each wavelength on a polarization component basis, while transmitting the same, and to output the respective separated polarization components in each wavelength in the same direction but along different optical axes; and said detection section having two line sensors (261, 262) detecting the interference polarization beams of each wavelength separated on a polarization component basis, respectively, the two sensor arrays being arranged side by side in parallel with a predetermined distance interval therebetween, and wherein the polarization optical element) has said entrance face slanted with respect to the traveling direction of the separated interference polarization beams when the separated interference polarization beams enter the polarization optical element; has a configuration in which each of separation distances is the same for all wavelengths, the separation distance being the distance from one separated interference polarization component to another separated interference polarization component in the identical wavelength; and wherein a thickness in a transmission direction in the polarization optical element through which the interference polarization beams transmit is different for each wavelength of the interference polarization beam, and gradually increases from a first lateral face side to a second lateral face side, the separated interference polarization beams with the shortest wavelength entering the entrance face of the first lateral face side, the separated interference polarization beams with wavelengths which are longer gradually from the first lateral face side to the second lateral face side, the separated interference polarization beam with the longest wavelength entering the entrance face of the second lateral face side. a diffraction grating adapted to separate the received interference polarization beam on a wavelength basis; a polarization optical element that has a birefringence characteristic including a first refractive index and a second refractive index, a lens that causes the interference polarization beams separated on a wavelength basis to be arranged in order of wavelengths from the first end to the second end of the entrance face of the polarization optical element, and causes such beams to enter the polarization optical element and a detection section; the polarization optical element being adapted to receive the separated interference polarization beams of the respective wavelengths in a wavelength order and in a parallel manner, to separate the separated interference polarization beam of each wavelength on a polarization component basis, while transmitting the same, and to output the respective separated polarization components in each wavelength in the same direction but along different optical axes; and said detection section having two line sensors (261, 262) detecting the interference polarization beams of each wavelength separated on a polarization component basis, respectively, the two sensor arrays being arranged side by side in parallel with a predetermined distance interval therebetween, and