  KAGRA is the first km-scale gravitational wave detector to be constructed
underground and employ cryogenics to cool down its test masses. While the
underground location provides a quiet site with low seismic noise, the cooling
infrastructure is known to generate large mechanical vibrations due to
cryocooler operation and structural resonances of the cryostat. As cooling
system components are relatively heavy and in close proximity to the test
masses, oscillation of gravity force induced by their vibration, so-called
Newtonian noise, could contaminate the detector sensitivity. In this paper, we
use the results from vibration analysis of the KAGRA cryostat to estimate
cooling system Newtonian noise in the 1-100 Hz frequency band. Our calculations
show that, while this noise does not limit the current detector sensitivity or
inspiral range, it will be an issue in the future when KAGRA improves its
sensitivity. We conclude that KAGRA may need to implement Wiener filters to
subtract this noise in the future.
