A tuning device for tuning a musical instrument to at least one target pitch, comprising: a converter converting vibrations representative of a tone produced in said musical instrument to an electric signal representative of said vibrations; an inspector (10, S20- S24, S26- S28) connected to said converter, and adapted for comparing an actual frequency of said tone with a target frequency of said at least one pitch to see whether or not said tone has said at least one target pitch for producing a positive answer indicative of the fact that said tone has said at least one target pitch or a negative answer indicative of the fact that said tone has a pitch different from said at least one target pitch; an image producer (10, 14, S29) connected to said inspector (10, S20-S24, S26- S28), and adapted for producing an image (32a, 32b, 32b") expressing said answer on a visual interface; and a resolution controller (10, S2, S10, S11, S25; 10, S30-S32) connected to said image producer (10, 14, S29) and adapted for requesting said image producer to vary a resolution of said image (32a, 32b, 32b"), characterized in that said image producer (10, 14, S29) is adapted to express a degree of the difference between said actual frequency and said target frequency through similarity between said image at the negative answer and said image at the positive answer so that said resolution controller (10, S2, S10, S11, S25; 10, S30 to S32) magnifies a part of said image at said negative answer when said actual frequency is assumed to get close to the target frequency, the magnification making said part of said image moved at higher speed than said part of said image before said magnification. a converter converting vibrations representative of a tone produced in said musical instrument to an electric signal representative of said vibrations; an inspector (10, S20- S24, S26- S28) connected to said converter, and adapted for comparing an actual frequency of said tone with a target frequency of said at least one pitch to see whether or not said tone has said at least one target pitch for producing a positive answer indicative of the fact that said tone has said at least one target pitch or a negative answer indicative of the fact that said tone has a pitch different from said at least one target pitch; an image producer (10, 14, S29) connected to said inspector (10, S20-S24, S26- S28), and adapted for producing an image (32a, 32b, 32b") expressing said answer on a visual interface; and a resolution controller (10, S2, S10, S11, S25; 10, S30-S32) connected to said image producer (10, 14, S29) and adapted for requesting said image producer to vary a resolution of said image (32a, 32b, 32b"), characterized in that said image producer (10, 14, S29) is adapted to express a degree of the difference between said actual frequency and said target frequency through similarity between said image at the negative answer and said image at the positive answer so that said resolution controller (10, S2, S10, S11, S25; 10, S30 to S32) magnifies a part of said image at said negative answer when said actual frequency is assumed to get close to the target frequency, the magnification making said part of said image moved at higher speed than said part of said image before said magnification.