provided are surface treatment agents that enable surfaces with a chemically fixed lubricant to be produced instead of a resin coating which has drawbacks , such as that lubricity is reduced due to separation , peeling or the like of the coating during the movement within a vessel or tube ; and medical devices , such as catheters , having a surface at least partially treated with such a surface treatment agent . the present invention relates to a surface treatment agent for medical devices which contains a copolymer of a hydrophilic functional group - containing monomer and an epoxy group - containing monomer .