  The Square Kilometre Array will revolutionize pulsar studies with its wide
field-of-view, wide-band observation and high sensitivity, increasing the
number of observable pulsars by more than an order of magnitude. Pulsars are of
interest not only for the study of neutron stars themselves but for their usage
as tools for probing fundamental physics such as general relativity,
gravitational waves and nuclear interaction. In this article, we summarize the
activity and interests of SKA-Japan Pulsar Science Working Group, focusing on
an investigation of modified gravity theory with the supermassive black hole in
the Galactic Centre, gravitational-wave detection from cosmic strings and
binary supermassive black holes, a study of the physical state of plasma close
to pulsars using giant radio pulses and determination of magnetic field
structure of Galaxy with pulsar pairs.
