The present invention provides a coating agent that has improved durability and a medical instrument (for example, a needle) that has been coated with said coating agent. This coating agent includes a hydroxyl-group-containing polyorganosiloxane (1) represented by general formula (1), a polydiorganosiloxane (2) represented by general formula (2), and an amino-group-containing polyorganosiloxane (3) represented by general formula (3). The mass ratio of the polydiorganosiloxane (2) to the amino-group-containing polyorganosiloxane (3) is 0.7-3.0. The hydroxyl-group-containing polyorganosiloxane (1) is included in a proportion of 2.4-5.5 mass pcnt with respect to the total mass of the hydroxyl-group-containing polyorganosiloxane (1), the polydiorganosiloxane (2), and the amino-group-containing polyorganosiloxane (3).
