A flow rate measurement device (100; 200) comprising: a flow rate measurer to measure a flow rate of a fluid at regular time intervals, the fluid flowing in a flow path; a period setting unit; and a fuel cell determinator to determine that a fuel cell is in operation; characterized in that: the period setting unit sets a first period corresponding to the time needed by flow rate measurer to perform M measurements, M being an integer greater than 1, and sets a second period made up of N first periods, N being an integer greater than 1; and the flow rate measurement device (100; 200) further comprises an arithmetic unit to calculate a first series of average flow rates of the M measured flow rates in each first period, and calculate a second series of average flow rates of the M x N measured flow rates in each second period; wherein the fuel cell determinator determines that a fuel cell is in operation when the first average flow rate series and the second average flow rate series calculated by the arithmetic unit satisfy all conditions A), B), and C) specified below: A) an increment between two successive values in the second average flow rate series within a first predetermined flow rate range repeats for a first predetermined number of successive times; B) an increment between two successive values in the first average flow rate series within a second predetermined flow rate range repeats for a second predetermined number of times or more in each of the second periods; and C) an increment between two successive values in the first average flow rate series is not greater than or equal to a third predetermined flow rate in each of the second periods. a flow rate measurer to measure a flow rate of a fluid at regular time intervals, the fluid flowing in a flow path; a period setting unit; and a fuel cell determinator to determine that a fuel cell is in operation; characterized in that: the period setting unit sets a first period corresponding to the time needed by flow rate measurer to perform M measurements, M being an integer greater than 1, and sets a second period made up of N first periods, N being an integer greater than 1; and the flow rate measurement device (100; 200) further comprises an arithmetic unit to calculate a first series of average flow rates of the M measured flow rates in each first period, and calculate a second series of average flow rates of the M x N measured flow rates in each second period; wherein the fuel cell determinator determines that a fuel cell is in operation when the first average flow rate series and the second average flow rate series calculated by the arithmetic unit satisfy all conditions A), B), and C) specified below: A) an increment between two successive values in the second average flow rate series within a first predetermined flow rate range repeats for a first predetermined number of successive times; B) an increment between two successive values in the first average flow rate series within a second predetermined flow rate range repeats for a second predetermined number of times or more in each of the second periods; and C) an increment between two successive values in the first average flow rate series is not greater than or equal to a third predetermined flow rate in each of the second periods. the period setting unit sets a first period corresponding to the time needed by flow rate measurer to perform M measurements, M being an integer greater than 1, and sets a second period made up of N first periods, N being an integer greater than 1; and the flow rate measurement device (100; 200) further comprises an arithmetic unit to calculate a first series of average flow rates of the M measured flow rates in each first period, and calculate a second series of average flow rates of the M x N measured flow rates in each second period; wherein the fuel cell determinator determines that a fuel cell is in operation when the first average flow rate series and the second average flow rate series calculated by the arithmetic unit satisfy all conditions A), B), and C) specified below: A) an increment between two successive values in the second average flow rate series within a first predetermined flow rate range repeats for a first predetermined number of successive times; B) an increment between two successive values in the first average flow rate series within a second predetermined flow rate range repeats for a second predetermined number of times or more in each of the second periods; and C) an increment between two successive values in the first average flow rate series is not greater than or equal to a third predetermined flow rate in each of the second periods. A) an increment between two successive values in the second average flow rate series within a first predetermined flow rate range repeats for a first predetermined number of successive times; B) an increment between two successive values in the first average flow rate series within a second predetermined flow rate range repeats for a second predetermined number of times or more in each of the second periods; and C) an increment between two successive values in the first average flow rate series is not greater than or equal to a third predetermined flow rate in each of the second periods.