To provide copper powder for copper paste used for setting an inter- layer conductive part of a printed wiring board which, with small resistance value, can surely be filled in a via hole or the like at the time of setting the inter-layer conductive part.

The copper powder for copper paste is a mixture of small particle-size spherical copper powder and large particle-size polyhedral copper powder. From such copper powder, copper paste with lower viscosity and low enough resistance is obtained. If viscosity of the copper powder is low, copper paste can be easily and surely filled in a via hole without any gaps, which gives an effect of securing conductive cross section area of an inter-layer conductive part of a printed wiring board and lowering resistance of the inter-layer conductive area.