The specification is related to a motor controller, a vehicle including the motor controller and a heat stress estimating method for a switching element. The motor controller includes a switching element, a temperature sensor, and a computer. The switching element is configured to convert output electric power of an electric power supply into motor-driving electric power. The temperature sensor is configured to measure a temperature of the switching element. The computer is configured to extract a maximum point and a minimum point in a time-dependent change in the temperature of the switching element, the computer is configured to calculate a temperature difference between the maximum point and the minimum point adjacent to each other and configured to calculate an estimated value of a heat stress to which the switching element is subjected based on each calculated temperature difference.