To provide a cell abnormality detection device capable of being composed at low cost by enhancing reliability of detection of abnormality of a cell constituting a fuel cell.

Each cell 3 of the fuel cell with a fuel gas passage 2a separated from an oxidizer gas passage 2b is composed by catching both sides of an electrolyte thin film 1 by a pair of gas separators 2, a fuel cell stack 4 is composed by stacking a plurality of the cells 3 in series, and a predetermined output voltage is provided by the stack 4. Each cell block 5 is formed by serially stacking a predetermined number of the cells 3, the cell stack 4 is composed by stacking a plurality of the cell blocks 5 in series, and the output voltages of the respective cell blocks 5 each having the same number of cells are compared with one another without previously defining an output voltage used as a reference, or the output voltages of the respective cell blocks 5 are compared by using the output voltage of a specific one of the cells 3 as a reference and by multiplying it by the number of the cells. A voltage comparator 8 is used for detecting presence of an abnormal one of the cells 3 in the fuel cell stack 4 by difference of its voltage to actuate a safety operation means 9.