A novel method of electrochemical treatment such as electroplating, etc.
and an electrochemical reaction apparatus thereof which is high in
reactability and able to be electrochemically reacted efficiently, which
is small or zero in amount of generation of liquid waste such as
electrolytic solution and cleaning liquid and therefore, amicable to the
environment, and in which it is no more required to clean the electrode,
etc. with cleaning liquid after reaction. Electrochemical reaction is
executed in a reaction vessel (6) containing matter (5) which is in a
supercritical or subcritical state and an electrolytic solution (1), and
after reaction, the supercritical or subcritical matter (5) is shifted
into a state of the matter (5) before being shifted into a critical state.
