We present resolved scattered-light images of the debris disk around HD 107146, a G2 star 28.5 pc from the Sun. This is the first debris disk to be resolved in scattered light around a solar-type star. We observed it with the HST/ACS coronagraph, using a 1.8 occulting spot and the F606W (broad V) and F814W (broad I) filters. Within 2 from the star, the image is dominated by PSF subtraction residuals. Outside this limit, the disk looks featureless except for a northeast-southwest brightness asymmetry that we attribute to forward scattering. The disk has scattered-light fractional luminosities of $(L_{Sca}/L_*)_{F606W}=6.8 pm 0.8 times 10^{-5}$ and $(L_{Sca}/L_*)_{F814W}=10 pm 1 times 10^{-5}$ and it is detected up to 6.5 away from the star. To map the surface density of the disk, we deproject it by $25^circ pm 5^circ$, divide by the dust scattering phase ($g_{F606W} = 0.3 pm 0.1$, $g_{F814W} = 0.2 pm 0.1$) and correct for the geometric dilution of starlight. Within the errors, the surface density has the same shape in each bandpass, and it appears to be a broad (85 AU) ring with most of the opacity concentrated at 130 AU. The ratio of the relative luminosity in F814W to that in F606W has the constant value of $1.3pm0.3$, with the error dominated by uncertainties in the value of $g$ in each filter. An examination of far infrared and submillimeter measurements suggests the presence of small grains. The colors and the derived values of $g$ are consistent with the presence of dust particles smaller than the radiation pressure limit. The dust generated by the creation of a small planet or the scattering and circularization of a large one, are possible scenarios that may explain the shape of the surface density profile.
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