The invention provides an optical imaging device, for realizing minimization and light weight of the optical imaging device. A measurement light emitted by a laser light source unit 1 and branched byan optical fiber into four is emitted into the space by an emitting unit 3 and bent upward by a reflecting mirror 4. A center of a sample table 5 where a biological sample 7 such as a mouse is mountedis a window where light can transmit, and the measurement light transmits the window of the sample table 5 and reaches a lower surface of the biological sample 7. A part of fluorescence excited by the measurement light and emitted passes the window, is bent by the reflecting mirror 4 in the opposite direction to the measurement light, and heads for a camera 12 for fluorescent photographing. Between the camera 12 and the reflecting mirror 4, an objective lens 10 for light condensation and a spectroscopic unit 11 for separating visible wavelength components are placed almost horizontally. Thus,irradiation of the measurement light and extraction of fluorescence are performed along a shaft extending in the vertical direction with respect to the biological sample 7, and optical components andelements can be placed side by side in the horizontal direction, so that an overall height of the device can be suppressed and its weight can be reduced.