We present new ALMA observations and physical properties of a Lyman Break Galaxy at z=7.15. Our target, B14-65666, has a bright ultra-violet (UV) absolute magnitude, $M_{rm UV}approx-22.4$, and has been spectroscopically identified in Ly$alpha$ with a small rest-frame equivalent width of $approx4$ AA. Previous HST image has shown that the target is comprised of two spatially separated clumps in the rest-frame UV. With ALMA, we have newly detected spatially resolved [OIII] 88 $mu$m, [CII] 158 $mu$m, and their underlying dust continuum emission. In the whole system of B14-65666, the [OIII] and [CII] lines have consistent redshifts of $7.1520pm0.0003$, and the [OIII] luminosity, $(34.4pm4.1)times10^{8}L_{rm odot}$, is about three times higher than the [CII] luminosity, $(11.0pm1.4)times10^{8}L_{rm odot}$. With our two continuum flux densities, the dust temperature is constrained to be $T_{rm d}approx50-60$ K under the assumption of the dust emissivity index of $beta_{rm d}=2.0-1.5$, leading to a large total infrared luminosity of $L_{rm TIR}approx1times10^{12}L_{rm odot}$. Owing to our high spatial resolution data, we show that the [OIII] and [CII] emission can be spatially decomposed into two clumps associated with the two rest-frame UV clumps whose spectra are kinematically separated by $approx200$ km s$^{-1}$. We also find these two clumps have comparable UV, infrared, [OIII], and [CII] luminosities. Based on these results, we argue that B14-65666 is a starburst galaxy induced by a major-merger. The merger interpretation is also supported by the large specific star-formation rate (defined as the star-formation rate per unit stellar mass), sSFR$=260^{+119}_{-57}$ Gyr$^{-1}$, inferred from our SED fitting. Probably, a strong UV radiation field caused by intense star formation contributes to its high dust temperature and the [OIII]-to-[CII] luminosity ratio.
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