A spectrometer capable of providing information, to a measurer, necessary for determining whether a sample set to the spectrometer is a sample expected by the measurer or not before a main measurement includes a data processor and a display. The data processor calculates a preliminary spectral information of the sample based on at least n of a latest detected signal and a BKG information retained in advance, calculates and updates the preliminary spectral information based on at least n of the latest detected signal and the BKG information again, and repeats these calculations and updates. The display shows the preliminary spectral information that is calculated and updated in the preview display. The data processor starts integration of N (N>n) of the detected signal during a preview display of the preliminary spectral information, and acquires a spectral information of the sample.