A viscosity measuring method and apparatus including (1) a step in which a plunger having an outer radius Ri is immersed into a sample in a container having an inner radius R0, by an initial depth L0; (2) a step in which the plunger is further immersed at a velocity vp1 by a distance ΔL1, and a force applied to the plunger is measured; (3) a step in which a peak value FT1 of the force is obtained; (4) a step in which the plunger is returned to the initial depth L0; (5) a step in which the plunger is further immersed at a velocity vp2 by a distance ΔL2, and a force applied to the plunger is measured; (6) a step in which a peak value FT2 of the force is obtained; (7) a step in which a flow behavior index n is obtained.