A magnetic core unit comprising: a wound magnetic core including a wound nanocrystalline alloy ribbon; a case having a space corresponding to an external shape of the wound magnetic core, the wound magnetic core being stored in the space; and an adhesive agent provided between a bottom surface of the space and a layered surface of the wound magnetic core, the adhesive agent adhering the wound magnetic core to the bottom surface, wherein the nanocrystalline alloy ribbon has a saturated magnetostriction of greater than 1 ppm, and magnetic permeability μ unit is not less than 400000 and Formula 1' and Formula 2' are satisfied: − 0.20 ≤ μ unit 100 − μ unit 25 / μ unit 25 ≤ 0 − 0.20 ≤ μ unit − 25 − μ unit 25 / μ unit 25 ≤ 0 where μ unit is a magnetic permeability measured at temperature T°C in the presence of an AC magnetic field of frequency f=50 Hz and amplitude H=1.0 ampere/meter (A/m) applied across the wound magnetic core adhered to the case, wherein the nanocrystalline alloy ribbon is made of an alloy which has a composition represented by Formula: (Fe 1-a M a) 100-x-y-z-α-β-γ Cu x Si y B z M' α M" β X γ (atomic %) (M is Co and/or Ni, M' is at least one element selected from the group consisting of Nb, Mo, Ta, Ti, Zr, Hf, V, Cr, Mn and W, M" is at least one element selected from the group consisting of Al, platinum group elements, Sc, rare-earth elements, Zn, Sn and Re, X is at least one element selected from the group consisting of C, Ge, P, Ga, Sb, In, Be and As, a, x, y, z, α, β and γ satisfy 0≤a≤0.5, 0.1≤x≤3, 0≤y≤30, 0≤z≤25, 5≤y+z≤30, 0≤α≤20, 0≤β≤20 and 0≤γ≤20, respectively), and characterized in that the layered surface of the wound magnetic core is adhered to the case by the adhesive agent in a range of not less than 30% and not more than 50% with respect to an area of the layered surface of the wound magnetic core. a wound magnetic core including a wound nanocrystalline alloy ribbon; a case having a space corresponding to an external shape of the wound magnetic core, the wound magnetic core being stored in the space; and an adhesive agent provided between a bottom surface of the space and a layered surface of the wound magnetic core, the adhesive agent adhering the wound magnetic core to the bottom surface, wherein the nanocrystalline alloy ribbon has a saturated magnetostriction of greater than 1 ppm, and magnetic permeability μ unit is not less than 400000 and Formula 1' and Formula 2' are satisfied: − 0.20 ≤ μ unit 100 − μ unit 25 / μ unit 25 ≤ 0 − 0.20 ≤ μ unit − 25 − μ unit 25 / μ unit 25 ≤ 0 where μ unit is a magnetic permeability measured at temperature T°C in the presence of an AC magnetic field of frequency f=50 Hz and amplitude H=1.0 ampere/meter (A/m) applied across the wound magnetic core adhered to the case, wherein the nanocrystalline alloy ribbon is made of an alloy which has a composition represented by Formula: (Fe 1-a M a) 100-x-y-z-α-β-γ Cu x Si y B z M' α M" β X γ (atomic %) (M is Co and/or Ni, M' is at least one element selected from the group consisting of Nb, Mo, Ta, Ti, Zr, Hf, V, Cr, Mn and W, M" is at least one element selected from the group consisting of Al, platinum group elements, Sc, rare-earth elements, Zn, Sn and Re, X is at least one element selected from the group consisting of C, Ge, P, Ga, Sb, In, Be and As, a, x, y, z, α, β and γ satisfy 0≤a≤0.5, 0.1≤x≤3, 0≤y≤30, 0≤z≤25, 5≤y+z≤30, 0≤α≤20, 0≤β≤20 and 0≤γ≤20, respectively), and characterized in that the layered surface of the wound magnetic core is adhered to the case by the adhesive agent in a range of not less than 30% and not more than 50% with respect to an area of the layered surface of the wound magnetic core.