Provided is a copper or copper alloy target/copper alloy backing plate assembly in which the anti-eddy current characteristics and other characteristics required in a magnetron sputtering target are simultaneously pursued in a well balanced manner. This copper or copper alloy target/copper alloy backing plate assembly is used for magnetron sputtering, and the copper alloy backing plate is formed from low beryllium copper alloy or Cu—Ni—Si-based alloy. Further, with this copper or copper alloy target/copper alloy backing plate assembly, the copper alloy backing plate has electrical conductivity of 35 to 60% (IACS), and 0.2% proof stress of 400 to 850 MPa.