1. A cooking appliance comprising:an electric heater configured to generate heat for cooking;
a mechanical manipulation unit that is electrically connected to the electric heater, the mechanical manipulation unit being configured to be manipulated by a user to directly control a primary ON/OFF state of the electric heater and a power level of the electric heater;
a normally open type DC relay that is electrically connected to the mechanical manipulation unit;
a child lock input unit configured to set or release a child lock; and
a controller that is configured to receive input from the child lock input unit and that is configured to, based on sensing a signal indicating that the mechanical manipulation unit controls the electric heater to be in the primary ON state, control the normally open type DC relay to control a secondary ON/OFF state of the electric heater based on whether the child lock has been set through the child lock input unit,
wherein the electric heater is configured to be activated based on both the primary ON/OFF state and the secondary ON/OFF state being controlled to be ON,
wherein the mechanical manipulation unit comprises a rotary switch configured to receive an angle input from the user, and a bimetal configured to directly control the power level of the electric heater by mechanically controlling a duty ratio of the electric heater based on the angle input to the rotary switch by the user, and
wherein the controller is further configured to disable the child lock input unit in a state in which the electric heater is driven.