A reactor comprises a first coil, a second coil and a core. Each of the first coil and the second coil is embedded in the core. The core has an outer core part, an inner core part, an upper core part, a lower core part and a middle core part. The upper core part is positioned above an upper end of a cross-section of the first coil in an up-down direction. The lower core part is positioned below a lower end of a cross-section of a second coil in the up-down direction. The core is made of a first member and a second member. The second member has a relative permeability which is greater than a relative permeability of the first member. Each of the upper core part and the lower core part is made of the second member.