A coolant heating apparatus includes: a housing having a coolant flow path therein and configured to cause coolant to flow into the housing and to flow out from the housing after being heated; a sheath heater provided in an inside of the housing and configured to heat the coolant; and a heat conduction plate provided inside the housing and made of a heat-conductive material. A portion of the heat conduction plate is bent in a shape to enclose an outer circumferential surface of the sheath heater and to be in surface contact with the sheath heater so as to carry out heat conduction with the sheath heater, and a remaining portion of the heat conduction plate is in surface contact with the coolant inside the housing such that the coolant is heated by heat conducted from the sheath heater.