The present invention provides a prophylactic or therapeutic agent, a pharmaceutical composition and a health-promoting food, which are used for human or other animal for the inhibition of the onset or progress of liver cancer, namely, an inhibitor of the onset or progress of liver cancer, which contains isoleucine, leucine and valine as active ingredients, wherein the weight ratio of isoleucine, leucine and valine is preferably 1:1.5 to 2.5:0.8 to 1.7 and the daily dose is 2.0 g to 50.0 g.