Provided are a surface roughening agent for aluminum and a surface roughening method using said surface roughening agent wherein it is possible to easily reduce costs for the surface roughening step and to improve the adhesiveness between aluminum and a resin. Specifically, provided is a surface roughening agent for aluminum comprising an aqueous solution containing: an alkali source, an amphoteric metal ion, a nitrate ion, and a thio compound. Moreover, provided is a surface roughening method for aluminum which involves a surface roughening step in which the surface of aluminum is treated with the aforementioned surface roughening agent.
