To restrain a phenomenon of a sheet of a lead alloy twisted around inside a manufacturing device during an expansion process.

While a belt-shaped lead alloy sheet is intermittently moved, expanding processing is carried out by a top blade 2 and a bottom blade 1 to manufacture an expanded metal grating. Here, a plurality of holes 3 are formed around the center of the bottom blade 1 in a length direction. Then, while compressed air 8 is blown in by a compressor toward a plain part 5 of the expanded grating 4 located upward from the holes 3 of the bottom blade 1, the lead alloy sheet subjected to the expanding processing.