NOVELTY - An apparatus (10) consists of tank (6) which accommodates acidic solution (1) containing acidic compound by definition of Arrhenius, and is equipped with working electrode (3) and reference pole (4), tank (7) which accommodates acidic solution (2) containing acidic compound at concentration higher than concentration in tank (6), and is provided with counter electrode (5) containing noble metal chosen from gold and platinum, and electric potential control mechanism.    USE - Apparatus is used for manufacturing core-shell catalyst (claimed) used for fuel cell.    ADVANTAGE - The apparatus enables economical manufacture of core-shell catalyst. Overvoltage at the time of electrode reaction is reduced.    DETAILED DESCRIPTION - An apparatus consists of tank (6) which accommodates acidic solution (1) containing acidic compound by definition of Arrhenius, and is equipped with working electrode and reference pole, tank (7) which accommodates acidic solution (2) containing acidic compound at concentration higher than concentration in tank (6), and is provided with counter electrode containing noble metal chosen from gold and platinum, and electric potential control mechanism which controls electric potential of the working electrode, reference pole and counter electrode. The tanks (6,7) are mutually separated by the cation exchange membrane (8). An INDEPENDENT CLAIM is included for manufacture of core-shell catalyst, which involves accommodating acidic solution containing acidic compound by definition of Arrhenius in tank (6) provided with reference pole and working electrode, providing noble metal in tank (7), mutually separating tanks (6,7) by cation exchange membrane, supplying base metal ion containing solution containing metal ion relatively more base than core metal material (9) and core metal to tank (6), depositing relative base metal on the surface of the core metal material by applying electric potential nobler than oxidation-reduction potential of relative base metal in the liquid mixture containing the base metal ion containing solution and acidic solution, and forming the shell by substituting relative base metal in shell metal by contacting shell metal-ion containing solution containing ion of shell metal with the core metal material in which the relative base metal is precipitated.    DESCRIPTION OF DRAWING(S) - The drawing shows cross-sectional view of the apparatus.    Acid solutions (1,2)    Working electrode (3)    Reference pole (4)    Counter electrode (5)    Tank (6,7)    Cation exchange membrane (8)    Core metal material (9)    Apparatus (10)