The electron temperature of a 915 MHz electron cyclotron resonance (ECR) plasma was controlled in a wide range by adjusting the incident microwave power when the gradient in the magnetic field strength near the resonant zone was gentle. From the numerical simulations of the microwave-power absorption, the electron temperature in an ECR plasma was found to change with changing spatial profiles of the power absorption. It was also suggested from our experimental and numerical results that the electron temperature is controlled by changing the gradient in the magnetic field strength and/or the microwave frequency because the power absorption profile may be changed with changing effective resonance zone width.