PURPOSE: To elevate the accuracy by interposing a means of fluidizing a liquid to be inspected, a capillary viscometer adapted to measure the viscosity of the liquid to be inspected according to the pressure on both sides of a tublet and a mass flowmeter capable of measuring mass flow rate and density in a passage of the liquid to be inspected.

CONSTITUTION: A tublet 11 is provided in a differential pressure converter 1 with each end communicating to outside thereof 1. Pressure receiving detectors 10 and 10' of a liquid sealed diaphragm type are arranged on the wall surface facing respective ends of the tublet 11. This viscometer is equipped with a viscosity receiver/recorder 8 and a mass flowmeter 2 connected to the tublet 11. A pump 3 is driven to run a liquid to be measured and then, a heat medium is fed into a jacket 17. This enables the measurement of the viscosity of the liquid based on the mass flow rate and the density signal from the mass flowmeter 2 and a differential pressure signal in pressures at both ends of the tublet.