Provided is a core which reduces optic splice loss between discontinuous optical waveguides. The core includes a first waveguide propagation portion having first light-receiving width, a first lightwave discontinuous portion having second light-receiving width, a first taper structure portion having both ends connected to the first lightwave propagation portion and to the first lightwave discontinuous portion, respectively and decreasing in light-receiving width as it goes from the first lightwave propagation portion to the first lightwave discontinuous portion, a second lightwave propagation portion having third light-receiving width, a second lightwave discontinuous portion having fourth light-receiving width, and a second taper structure portion having both ends connected to the second lightwave propagation portion and to the second lightwave discontinuous portion, respectively and decreasing in light-receiving width as it goes from the second lightwave propagation portion to the second lightwave discontinuous portion.