A pressure measuring device 30 installs on a tube 11 for transferring a medium (e.g., blood in a extracorporeal blood circulator) so as to measure a pressure of the medium inside the tube 11. The pressure measuring device 30 includes a main body portion 31 mountable to the tube 11, an image acquisition unit 32 disposed in the main body portion 31 so as to acquire image information on a pressure receiver that is deformed in response to the received pressure of the medium inside the tube 11, and a control unit 100 that converts the image information acquired by the image acquisition unit into pressure information about the pressure.
