PURPOSE: To obtain a multi-needles electrode device having a reduced number of parts and high workabilities for assembling while keeping a reduced probability of being produced as rejected products by making an outer casing holding the multi- needles electrode assemblies and consisting of a combination of a main frame and a lid therefor having a same configuration.

CONSTITUTION: Needle electrode assemblies 3 are inserted into a main frame 2 of a casing and are determined the locations thereof by protuberances 2b1p, 2b2p, 2ap formed on the main frame 2, thereafter, are fixed to a bottom plate portion 2a by screws through apertures p1W94. Next, a printed circuit board 4 is inserted and fixed within the main frame 2. One ends of respective withdrawn wires of flat cables 51W53 are connected to electrodes of the printed circuit board 4, then, a lid 1 of the casing, having a same configuration as the main frame 2, is put thereon and is connected to the multi-needles electrode assemblies 3 and the main frame 2 integrally by screws 61W64, 71W74, while the flat cables 51W53 are held by securing between recessed portions 2cR1W2cR3.