By intracerebroventricularly administering relaxin-3 binding to SALPR to rat s and observing feed intake, body weight, fat amount, etc. of the animals afte r the administration, it is found out that relaxin-3 has useful effects of promoting food intake, promoting body weight gain and causing obesity. Thus, it is possible to provide a polypeptide having useful effects of promoting food intake, promoting body weight gain and causing obesity a remedy for diseases containing this polypeptide a method of screening a compound, a substance or a salt thereof activating or inhibiting a receptor of the polypeptide a screening kit therefor and a food intake regulating agent, a remedy for obesity, a remedy for diabetes and so on containing a substance inhibiting the expression of the polypeptide, etc.