A non-excitation operable electromagnetic brake comprising: a spring for operating a rotor into a braking state; an electromagnet configured, under an excited state thereof, to operate the rotor into a brake releasing state against the spring; a rotary cam manually and rotationally operable between an acting position for slidably operating the rotor into the brake releasing state against the spring under the non-excited state of the electromagnet and a releasing position for releasing a slidable operation of the rotor, thus allowing an operation of the rotor into the brake releasing state by the electromagnet a rotation restriction portion configured to restrict rotation of the rotary cam from the releasing position in a rotational direction opposite to a set rotational direction which is set for switching the rotary cam from the releasing position to the acting position; and a positioning mechanism capable of switchover between a positioning state for fixedly positioning an operational tool for rotating the rotary cam to operational positions corresponding respectively to the releasing position and the acting position and a position releasing state for allowing an operation of the operational tool, wherein in a circumferential cam of the rotary cam, an acting portion thereof corresponding to the acting position is formed linear along a tangent at a center of the acting portion with respect to a rotary cam rotational direction; and characterized in that: the positioning mechanism includes an engaging portion protruding downwards from a base portion of the operational tool and a positioning portion provided in an outer circumference of a brake case at a portion thereof opposed to the base portion of the operational tool; the positioning portion includes a first receded portion for positioning the operational tool at the acting position and a second receded portion for positioning the operational tool at the releasing position; and positioning of the operational tool is provided by engagement of the engaging portion in the first receded portion or the second receded portion. a spring for operating a rotor into a braking state; an electromagnet configured, under an excited state thereof, to operate the rotor into a brake releasing state against the spring; a rotary cam manually and rotationally operable between an acting position for slidably operating the rotor into the brake releasing state against the spring under the non-excited state of the electromagnet and a releasing position for releasing a slidable operation of the rotor, thus allowing an operation of the rotor into the brake releasing state by the electromagnet a rotation restriction portion configured to restrict rotation of the rotary cam from the releasing position in a rotational direction opposite to a set rotational direction which is set for switching the rotary cam from the releasing position to the acting position; and a positioning mechanism capable of switchover between a positioning state for fixedly positioning an operational tool for rotating the rotary cam to operational positions corresponding respectively to the releasing position and the acting position and a position releasing state for allowing an operation of the operational tool, wherein in a circumferential cam of the rotary cam, an acting portion thereof corresponding to the acting position is formed linear along a tangent at a center of the acting portion with respect to a rotary cam rotational direction; and characterized in that: the positioning mechanism includes an engaging portion protruding downwards from a base portion of the operational tool and a positioning portion provided in an outer circumference of a brake case at a portion thereof opposed to the base portion of the operational tool; the positioning portion includes a first receded portion for positioning the operational tool at the acting position and a second receded portion for positioning the operational tool at the releasing position; and positioning of the operational tool is provided by engagement of the engaging portion in the first receded portion or the second receded portion. the positioning mechanism includes an engaging portion protruding downwards from a base portion of the operational tool and a positioning portion provided in an outer circumference of a brake case at a portion thereof opposed to the base portion of the operational tool; the positioning portion includes a first receded portion for positioning the operational tool at the acting position and a second receded portion for positioning the operational tool at the releasing position; and positioning of the operational tool is provided by engagement of the engaging portion in the first receded portion or the second receded portion.