A pressure measuring device 30 installs on a tube 11 for transferring a medium BL so as to measure a pressure of the medium BL inside the tube 11. The pressure measuring device 30 includes a main body portion 31 mountable to the tube 11, polarizing means 34 disposed in the main body portion 31 so that light oscillating in a specific direction is transmitted therethrough, an image acquisition unit 32 disposed in the main body portion 31 so that image information on a pressure receiver that is deformed in response to the received pressure is acquired through the polarizing means 34, and a control unit 100 that converts the image information acquired by the image acquisition unit 32 into pressure information about the pressure.
