A microorganism represented by a strain K04-0144 belonging to Streptomyces sp. having ability to produce K04-0144 substance is cultured in the medium, and the isolated K04-0144A substance, K04-0144B substance and K04-0144C substance therefrom have strong antibacterial activities against Gram-positive bacteria including methicillin-resistant Streptococcus aureus (MRSA), consequently these are useful as the therapeutic agents for infectious disease caused by MRSA as well as infectious diseases caused by multidrug including β-lactam antibiotics resistant bacteria. Further, similarly, since the novel K04-0144D substance isolated from the cultured liquid has the action for enhancing the effect of β-lactam antibiotics, which are utilized as the antibacterial agents, in combination with them, it is useful as the therapeutic agent for infectious diseases caused by methicillin-resistant Staphylococcus aureus (MRSA) and multidrug including β-lactam antibiotics resistant bacteria.