  Combining the Solar Dynamics Observatory and the New Vacuum Solar Telescope
observations, we study a confined flare triggered by a rising flux rope within
the trailing sunspots of active region 12733. The flux rope lying above the
sheared polarity inversion line can be constructed through magnetic
extrapolation but could not be detected in multi-wavelength images at the
pre-flare stage. The conspicuous shearing motions between the opposite-polarity
fields in the photosphere are considered to be responsible for the flux rope
formation. The maximum twist of the flux rope is as high as -1.76, and then the
flux rope rises due to the kink instability. Only when the flare starts can the
flux rope be observed in high-temperature wavelengths. The differential
emission measure results confirm that this flux rope is a high-temperature
structure. Associated with the rising flux rope, there appear many post-flare
loops and a pair of flare ribbons. When the rising flux rope meets and
reconnects with the large-scale overlying field lines, a set of large-scale
twisted loops are formed, and two flare ribbons propagating in opposite
directions appear on the outskirts of the former ribbons, indicating that the
twist of the flux rope is transferred to a much larger system. These results
imply that the external reconnection between the rising flux rope and the
large-scale overlying loops plays an important role in the confined flare
formation.
