A breaker apparatus comprises: a breaker switch including a pair of fixed electrodes standing upright on the breaker body, a plug detachably mounted on the breaker body, and a movable electrode provided on the plug for disconnecting and connecting between both fixed electrodes by being pulled out or pushed in to the both fixed electrodes; and a fuse mounted in parallel with the breaker switch, characterized in that a locking lever is pivotably mounted on one of the breaker body and the plug and the locking lever is pivoted to the locking position where the plug is locked in the fitted state, in that the breaker body is provided with a micro switch having a swinging strip for detecting whether or not the locking lever is pivoted to the locking position so that the micro switch is activated when the tip of the locking lever pivots along the length of the swinging strip and presses the swinging strip on the way to activate the micro switch, and in that the tip of the locking lever is formed so that the length is maximum at the rear edge that trails when the locking lever is pivoted toward the locking position and decreases gradually toward the leading edge.