We propose a measurement of spin excitation in heavily underdoped Bi2201 at MERLIN with intent to elucidate an origin of "hourglass" excitation in hole-doped cuprates. Recent our measurement on Bi2201 shows a similarity and difference in the doping dependence of low-energy excitation with LSCO, which might be originated from pseudo-gap phenomena and/or itinerancy of electron. This provides important opportunity to explore the generic feature of spin excitation. We would like to investigate a wide range excitation spectrum in the target system and clarify the characteristic doping evolution from a comparison with previously obtained result for the optimally-doped sample. Since ARPES measurements were intensively performed on Bi2201, we expect that our neutron-scattering results will provide important information to understand the interplay between spin and charge degree of freedoms.