A cell observation system 1, for measuring fluorescence emitted from a cell held by a microplate 20 having a plurality of wells 21, comprises a microplate holder 11 for mounting the microplate 20, an electrical stimulator 16 arranged with a plurality of electrode pairs 17 including positive and negative electrodes 17b, 17a, a position controller 30 for controlling a position of the electrical stimulator 16 so as to place the electrode pairs 17 within the wells 21, a moving image acquisition unit 40 for detecting the fluorescence from the sample S within the wells 21, and a data analyzer 50 for setting a part of a region facing the positive electrode 17b on the well 21 as an analysis region and analyzing an optical intensity in the analysis region so as to acquire analysis information concerning the sample S.