A rotating electrical machine includes a plurality of core pieces forming a stator core. Each of the core pieces includes contact surfaces on one side end and another side end in a peripheral direction, a tapered protrusion on the contact surface of the one side end, the protrusion including first inclined surfaces outside and inside, and a recess on the contact surface of the other side end, the recess including second inclined surfaces contacting the first inclined surfaces outside and inside to receive the protrusion of adjacent core piece. A cross-sectional shape of the protrusion is a shape such that, inside a circle centered on a first end portion with a distance being a radius between a second end portion located on an opposite side of the first end portion and the first end portion, at least a part of the first inclined surfaces contact the second inclined surfaces.