To provide a novel boron-containing compound. A compound represented by the following formula: wherein black circle represents B, white circles represent B-H； -Rrepresents -(CH)n-X-R(n represents an integer of 0 to 6； Xrepresents O, S, NH, S-S, O-CO, NHCO or SCO, or does not exist； Rrepresents C-Calkyl, hydroxy C-Calkyl, amino C-Calkyl, azido C-Calkyl, hydroxycarbonyl C-Calkyl, or the like), or a group having a repeating sequence of -(CH)-O- 3 times or more and 10 times or less and having a methyl group or an ethyl group at the end on the oxygen atom side； and -Ris - (CH)m-X-R(m represents an integer from 0 to 8； Xrepresents O, S, NH, S-S, O-CO, NHCO or SCO, or does not exist； and Rrepresents a tumor recognition moiety), or does not exist are prepared and used.
