A cell observation system 1 is a cell observation system 1 for observing a cell held by a microplate 20 having a plurality of wells 21 arranged therein for holding a sample S including the cell and 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, and a data analyzer 50 for controlling a position of the electrical stimulator 16 so as to place the electrode pairs 17 within the wells 21 of the microplate 20, while a leading end of the negative electrode 17a on the well 21 side extends longer than a leading end of the positive electrode 17b on the well 21 side.