Heat exchanger and method for hydrophilizing heat exchanger

A heat exchanger having a hydrophilic coating on a surface of an aluminum base material of the heat exchanger,

• the hydrophilic coating being formed using a hydrophilizing agent, wherein the hydrophilic coating comprises:
• 90% by mass or more of a resin (D);
• and
• 0.8 to 1.8% by mass of a vanadium compound (E), calculated based on a vanadium element, wherein
• the resin (D) comprises:
• 38 to 40% by mass of polyvinyl alcohol (A) having an ethylene chain;
• 22 to 24% by mass of a structure unit derived from a radically polymerizable monomer (B1) having a carboxylic acid;
• 15 to 17% by mass of a structure unit derived from a radically polymerizable monomer (B2) represented by Formula (1) below:
• CH2═C(R1)CO—(OCH2CH2)m-OR2 (1)
• where R1 represents H or CH3, R2 represents H or CH3, and m represents an integer from 1 to 200;
• and
• 22 to 24% by mass of polyethylene glycol (C).