There is provided a bubble column type hydrocarbon synthesis reactor which synthesizes a hydrocarbon compound by a chemical reaction of a synthesis gas including hydrogen and carbon monoxide as main components, and a slurry having solid catalyst particles suspended in liquid. The hydrocarbon synthesis reactor includes a reactor main body which accommodates the slurry, a synthesis gas supplying section which supplies the synthesis gas to the slurry; one pressure sensor which is arranged higher than the liquid level of the slurry to measure the pressure of the synthesis gas above the liquid level, another pressure sensor which is arranged lower than the liquid level of the slurry to measure the pressure of the slurry, and a liquid level detecting device which detects a liquid level position of the slurry on the basis of measurement results of the pressure sensors. A plurality of the other pressure sensors are provided at arbitrary intervals in an axial direction of the reactor main body.