PURPOSE: To miniaturize the title apparatus as a whole by measuring a flow rate and concn. by one measuring piping by connecting the measuring piping to piping through which a fluid to be measured flows and providing a transmission probe and a plurality of receiving probes to the predetermined part of the measuring piping.

CONSTITUTION: A transmission probe 5 and receiving probes 7, 6 for respectively measuring a flow rate (time lag) and concn. (attenuation quantity) are provided to one measuring piping 4 connected to piping 1 and the probe 5 is driven by one drive part 8 in a sensor part 3. In a flow rate measuring part 9, the ultrasonic transmission signal outputted from the drive part 8 and the ultrasonic receiving signal passed through a fluid to be measured to be outputted from the probe 7 are taken in a receiving circuit 13 to count the ultrasonic propagation time of the fluid to be measured flowing through the piping 4 by a counter circuit 14 and this propagation time is converted to a flow rate signal by an output conversion circuit 15 to be outputted to the outside. A concn. measuring part 10 takes in the ultrasonic transmission signal outputted from the drive part 8 and the ultrasonic receiving signal outputted from the probe 6 to operate ultrasonic attenuation quantity by an ultrasonic attenuation quantity operation part 16 and an attenuation quantity signal is amplified by an amplifying circuit 17 to be converted to a concn. signal by an output conversion circuit 18 to output the concn. signal.