A dust core comprising: a plurality of soft magnetic particles composed of an iron-based material; an insulating layer including a coating layer that is composed mainly of a phosphate and covers the surface of the soft magnetic particles; and insulating pieces containing a constituent material of the insulating layer, each of the insulating pieces being surrounded by at least three mutually adjacent ones of the soft magnetic particles while separated from the insulating layer, wherein: the coating layer has an average thickness of from 30 nm to 120 nm inclusive; the insulating layer further includes an outer layer formed outward of the coating layer; the outer layer is composed mainly of one compound selected from a silicate compound composed mainly of Si and O, a magnesium oxide composed mainly of Mg and O, a titanium oxide composed mainly of Ti and O, and an aluminum oxide composed mainly of Al and O; the outer layer has an average thickness of from 10 nm to 100 nm inclusive; the insulating pieces have a size of from 0.3 μm to 5.0 μm, the size being the longitudinal length of a strip-shaped piece observed in an image of a cross section of the dust core under an SEM, the size being determined by observing 100 regions which are surrounded by at least three mutually adjacent soft magnetic particles and in which an insulating piece is observed, the size being the average of the lengths of the strip shaped insulating prices in the regions; and the presence ratio of the insulating pieces is from 5% to 90%, the presence ratio being determined by observing 100 regions surrounded by at least three mutually adjacent soft magnetic particles, the presence ratio being the number of regions in which an insulating piece is present. a plurality of soft magnetic particles composed of an iron-based material; an insulating layer including a coating layer that is composed mainly of a phosphate and covers the surface of the soft magnetic particles; and insulating pieces containing a constituent material of the insulating layer, each of the insulating pieces being surrounded by at least three mutually adjacent ones of the soft magnetic particles while separated from the insulating layer, the coating layer has an average thickness of from 30 nm to 120 nm inclusive; the insulating layer further includes an outer layer formed outward of the coating layer; the outer layer is composed mainly of one compound selected from a silicate compound composed mainly of Si and O, a magnesium oxide composed mainly of Mg and O, a titanium oxide composed mainly of Ti and O, and an aluminum oxide composed mainly of Al and O; the outer layer has an average thickness of from 10 nm to 100 nm inclusive; the insulating pieces have a size of from 0.3 μm to 5.0 μm, the size being the longitudinal length of a strip-shaped piece observed in an image of a cross section of the dust core under an SEM, the size being determined by observing 100 regions which are surrounded by at least three mutually adjacent soft magnetic particles and in which an insulating piece is observed, the size being the average of the lengths of the strip shaped insulating prices in the regions; and the presence ratio of the insulating pieces is from 5% to 90%, the presence ratio being determined by observing 100 regions surrounded by at least three mutually adjacent soft magnetic particles, the presence ratio being the number of regions in which an insulating piece is present.