aluminum alloy the anode connector 11 is formed of the same metal as the negative terminal 6 that is copper or copper alloy the boundary between the cathode connector 10 and the anode connector 11 of the busbar 1 is formed by placing the metal of the cathode connector 10 al and the metal of the anode connector 11 cu under an ultrahigh pressure for example about 1 000 mpa and causing deformation thereof the metals are bonded so as to form a bonding interface in which they are tightly bonded at the metal structural level so that the conductivity and mechanical bonding strength are increased to u201c values suitable for a busbar in practical use u201d as illustrated in fig2 a and 2b a connection hole 12 that allows the positive terminal 5 of each battery cell 2 to be inserted therethrough is formed in the cathode connector 10 at substantially the central position in the short side direction thereof similarly a connection hole 13 that allows the negative terminal 6 of each battery cell 2 to be inserted therethrough is formed in the anode connector 11 at substantially the central position in the short side direction thereof referring to fig1 each cathode connector 10 is connected to the corresponding positive terminal 5 by inserting the positive terminal 5 through the connection hole 12 and engaging a nut 15 with the positive terminal 5 that projects from the connection hole.