Neutron is a chargeless massive particle with the lifetime in the macroscopic range,
which consequently is suitable for the precision measurement of the small influence
of new physics beyond the standard model of elementary particles.
The neutron lifetime is one of the key parameters for the big-bang nucleosynthesis.
In-flight measurement with the accuracy of 0.1 % is required.
The permanent electric dipole moment of neutrons signals the breaking of
time-reversal invariance. The best upper limit is very close to the predictions of
some of new physics.
Combination of the instantaneousely luminous cold neutrons at J-PARC and the
advanced neutron optical devices enables us to perform new types of high
precision measurements. In this talk the present status of our approach to the
fundamental physics with neutrons will be reported.