Specifically acts as an arginine mono-ADP-ribosylhydrolase by mediating the removal of mono-ADP-ribose attached to arginine residues on proteins. H2O + N(omega)-(ADP-D-ribosyl)-L-arginyl-[protein] = ADP-D-ribose + L-arginyl-[protein] Binds 2 magnesium ions per subunit. Monomer. Belongs to the ADP-ribosylglycohydrolase family.