A flow meter device comprising: a flow measuring section which includes a pair of ultrasonic transducers (11, 12) which are placed so as to face each other in a direction crossing a measurement fluid passage through which a fluid as a measurement target flows, and is configured to measure a flow of the fluid by transmitting and receiving an ultrasonic wave between the ultrasonic transducers (11, 12); and wherein the flow measuring section includes a flow calculating section including a measurement block flow calculating section and a sampling cycle flow calculating section; wherein the flow meter device further comprises a measurement control section which is configured to control the flow measuring section such that the flow measuring section measures the flow of the fluid in each sampling cycle (Tc) set as a minimum time unit at which the flow of the fluid is measured; wherein the measurement control section includes a transmission/reception control section, a sampling cycle setting section and a measurement block dividing section; wherein the measurement control section is configured to divide the sampling cycle (Tc) into three or more measurement blocks (Tb) of an equal length and causes the flow measuring section to measure the flow of the fluid in each of the measurement blocks (Tb); and wherein the flow measuring section is configured to calculate an average value of flow values obtained in all of the measurement blocks (Tb) in each sampling cycle (Tc), as a flow value in each sampling cycle (Tc); characterized in that when a flow value measured in a sampling cycle (Tc) is a cycle flow value, and a flow value measured in each of three or more measurement blocks (Tb) into which the sampling cycle (Tc) is divided is a block flow value, the cycle flow value is calculated as an average value of block flow values in a single sampling cycle (Tc). a flow measuring section which includes a pair of ultrasonic transducers (11, 12) which are placed so as to face each other in a direction crossing a measurement fluid passage through which a fluid as a measurement target flows, and is configured to measure a flow of the fluid by transmitting and receiving an ultrasonic wave between the ultrasonic transducers (11, 12); and wherein the flow measuring section includes a flow calculating section including a measurement block flow calculating section and a sampling cycle flow calculating section; wherein the flow meter device further comprises a measurement control section which is configured to control the flow measuring section such that the flow measuring section measures the flow of the fluid in each sampling cycle (Tc) set as a minimum time unit at which the flow of the fluid is measured; wherein the measurement control section includes a transmission/reception control section, a sampling cycle setting section and a measurement block dividing section; wherein the measurement control section is configured to divide the sampling cycle (Tc) into three or more measurement blocks (Tb) of an equal length and causes the flow measuring section to measure the flow of the fluid in each of the measurement blocks (Tb); and wherein the flow measuring section is configured to calculate an average value of flow values obtained in all of the measurement blocks (Tb) in each sampling cycle (Tc), as a flow value in each sampling cycle (Tc); characterized in that when a flow value measured in a sampling cycle (Tc) is a cycle flow value, and a flow value measured in each of three or more measurement blocks (Tb) into which the sampling cycle (Tc) is divided is a block flow value, the cycle flow value is calculated as an average value of block flow values in a single sampling cycle (Tc).