An image acquiring device comprises a first camera 14 for acquiring video images, consisting of frame images continuous in time series, a second camera 15 being in a known relation with the first camera and used for acquiring two or more optical spectral images of an object to be measured, and an image pickup control device 21, and in the image acquiring device, the image pickup control device is configured to extract two or more feature points from one of the frame images, to sequentially specify the feature points in the frame images continuous in time series, to perform image matching between the frame images regarding the frame images corresponding to the two or more optical spectral images based on the feature points, and to synthesize the two or more optical spectral images according to the condition obtained by the image matching.