Provided is a new therapeutic agent for a malignant tumor, which is highly safe, sustains an antitumor effect, and can improve the means for administration and the number of times of administration. Disclosed is a compound of Formula (1), or a salt thereof: €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒC[CH 2 O(CH 2 CH 2 O) m CH 2 CO-R 1 -R 2 ] 4 €ƒ€ƒ€ƒ€ƒ€ƒ(1) wherein R 1 represents a single bond, -N(R 3 ) (CH 2 ) n1 CO-, or -N(R 4 ) (CH 2 ) n2 N(R 5 )CO(CH 2 ) n3 CO-； R 2 represents a group of Formula (a), (b), (c), (d), (e), or (f): m represents a number of from 10 to 1,000； and an arrow represents a bonding site.
