An observation device comprising: a light source for irradiating a moving object with light (L 0); a detection unit, letting a first direction be a direction on a predetermined plane yielding a fixed Doppler shift effect caused by a movement of the object in light (L 0) having reached the predetermined plane in scattered light (L 1) generated by the object upon irradiation with the light (L 0) by the light source while being perpendicular to a moving direction of the object and a second direction be a direction orthogonal to the first direction on the predetermined plane while being parallel to the moving direction of the object, for outputting data representing a sum in the second direction of data temporally changing at a frequency corresponding to a Doppler shift frequency of the light having reached each position on the predetermined plane at each position in the first direction at each time; and an arithmetic unit for performing a one-dimensional Fourier transform of data employing the position in the first direction on the predetermined plane and time as variables with respect to a time variable and a two-dimensional Fourier transform of the Fourier-transformed data, so as to yield data obtained by the two-dimensional Fourier transform as an image of the object; wherein the detection unit includes: an optical system for receiving a light (L 0) emitted from the light source and splitting the received light in two so as to yield first light and second light, irradiating the object with the first light, modulating the second light with a modulator, and then causing a heterodyne interference between the scattered light and the modulated second light on the predetermined plane; and a photodetector having a light-receiving surface on the predetermined plane and a pixel array structure in the first direction on the light-receiving surface. a light source for irradiating a moving object with light (L 0); a detection unit, letting a first direction be a direction on a predetermined plane yielding a fixed Doppler shift effect caused by a movement of the object in light (L 0) having reached the predetermined plane in scattered light (L 1) generated by the object upon irradiation with the light (L 0) by the light source while being perpendicular to a moving direction of the object and a second direction be a direction orthogonal to the first direction on the predetermined plane while being parallel to the moving direction of the object, for outputting data representing a sum in the second direction of data temporally changing at a frequency corresponding to a Doppler shift frequency of the light having reached each position on the predetermined plane at each position in the first direction at each time; and an arithmetic unit for performing a one-dimensional Fourier transform of data employing the position in the first direction on the predetermined plane and time as variables with respect to a time variable and a two-dimensional Fourier transform of the Fourier-transformed data, so as to yield data obtained by the two-dimensional Fourier transform as an image of the object; wherein the detection unit includes: an optical system for receiving a light (L 0) emitted from the light source and splitting the received light in two so as to yield first light and second light, irradiating the object with the first light, modulating the second light with a modulator, and then causing a heterodyne interference between the scattered light and the modulated second light on the predetermined plane; and a photodetector having a light-receiving surface on the predetermined plane and a pixel array structure in the first direction on the light-receiving surface. an optical system for receiving a light (L 0) emitted from the light source and splitting the received light in two so as to yield first light and second light, irradiating the object with the first light, modulating the second light with a modulator, and then causing a heterodyne interference between the scattered light and the modulated second light on the predetermined plane; and a photodetector having a light-receiving surface on the predetermined plane and a pixel array structure in the first direction on the light-receiving surface.