A planar elongational viscosity measuring method and apparatus which can advance analysis of planar elongational viscosities for high-viscosity and low-viscosity fluids. As a bomb-shell like bob 2 is pushed into a container 6, a non-Newtonian fluid 9 reaches a planar elongation state in a side space G, counterforce F applied to the bomb-shell like bob 2 at this time is measured, planar elongation stress τ is calculated using the counterforce F and conditions input by a user based on push-up force, the counterforce F, and the horizontal cross-sectional area of the side space G, and the planar elongation stress is divided by a planar elongation speed ε′, thereby acquiring a planar elongational viscosity ηPE. Accordingly, it becomes possible to acquire planar elongational viscosities of not only a high-viscosity non-Newtonian fluid, but also a low-viscosity non-Newtonian fluid which is not likely to be solidified, resulting in an advancement of analysis of planar elongational viscosities for high-viscosity and low-viscosity fluids.
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