A holographic display device comprising: a light source configured to emit a plurality of color lights (L R, L G, L B); a focus modulation optical system (150, 200, 200A, 400) comprising at least one variable focus lens (210, 220, 230; 301, 302, 303; 420) that is configured to change a focusing position of incident light by electrical control of the at least one variable focus lens (210, 220, 230; 301, 302, 303; 420) based on a color of light incident on the at least one variable focus lens (210, 220, 230; 301, 302, 303; 420), wherein the at least one variable focus lens (210, 220, 230; 301, 302, 303; 420) is variable such that each color light (L R, L G, L B) forms a focus at a same position; and a spatial light modulator configured to form a holographic image, characterized in that the spatial light modulator is configured to form the holographic image by diffracting light output from the focus modulation optical system (150, 200, 200A, 400); wherein the at least one variable focus lens (210, 220, 230; 301, 302, 303; 420) comprises: a first variable focus lens (210; 301) configured to focus first color light (L R) at a first position; a second variable focus lens (220; 302) configured to focus second color light (L G) at the first position; and a third variable focus lens (230; 303) configured to focus third color light (L B) at the first position, wherein the first variable focus lens (210; 301), the second variable focus lens (220; 302), and the third variable focus lens (230; 303) are sequentially disposed; and wherein the holographic display device further comprises: a first wavelength selective retarder (205; 305) provided in front of the first variable focus lens (210; 301); a second wavelength selective retarder (215; 306) provided between the first variable focus lens (210; 301) and the second variable focus lens (220; 302); and a third wavelength selective retarder (225; 307) provided between the second variable focus lens (220; 302) and the third variable focus lens (230; 303). a light source configured to emit a plurality of color lights (L R, L G, L B); a focus modulation optical system (150, 200, 200A, 400) comprising at least one variable focus lens (210, 220, 230; 301, 302, 303; 420) that is configured to change a focusing position of incident light by electrical control of the at least one variable focus lens (210, 220, 230; 301, 302, 303; 420) based on a color of light incident on the at least one variable focus lens (210, 220, 230; 301, 302, 303; 420), wherein the at least one variable focus lens (210, 220, 230; 301, 302, 303; 420) is variable such that each color light (L R, L G, L B) forms a focus at a same position; and a spatial light modulator configured to form a holographic image, characterized in that the spatial light modulator is configured to form the holographic image by diffracting light output from the focus modulation optical system (150, 200, 200A, 400); wherein the at least one variable focus lens (210, 220, 230; 301, 302, 303; 420) comprises: a first variable focus lens (210; 301) configured to focus first color light (L R) at a first position; a second variable focus lens (220; 302) configured to focus second color light (L G) at the first position; and a third variable focus lens (230; 303) configured to focus third color light (L B) at the first position, a first variable focus lens (210; 301) configured to focus first color light (L R) at a first position; a second variable focus lens (220; 302) configured to focus second color light (L G) at the first position; and a third variable focus lens (230; 303) configured to focus third color light (L B) at the first position, wherein the first variable focus lens (210; 301), the second variable focus lens (220; 302), and the third variable focus lens (230; 303) are sequentially disposed; and wherein the holographic display device further comprises: a first wavelength selective retarder (205; 305) provided in front of the first variable focus lens (210; 301); a second wavelength selective retarder (215; 306) provided between the first variable focus lens (210; 301) and the second variable focus lens (220; 302); and a third wavelength selective retarder (225; 307) provided between the second variable focus lens (220; 302) and the third variable focus lens (230; 303). a first wavelength selective retarder (205; 305) provided in front of the first variable focus lens (210; 301); a second wavelength selective retarder (215; 306) provided between the first variable focus lens (210; 301) and the second variable focus lens (220; 302); and a third wavelength selective retarder (225; 307) provided between the second variable focus lens (220; 302) and the third variable focus lens (230; 303).