An electroless copper plating bath containing a cupric compound, a cupric ion complexing agent, a reducing agent, and a pH adjusting agent is provided, in which a carboxylic acid is added as a reaction accelerator to accelerate the oxidation reaction of the reducing agent. It does not need to use formaldehyde as the reducing agent yet it has a plating reaction velocity which is equivalent to that of a bath in which formaldehyde is contained as the reducing agent.