SN1997ap at z=0.83 was discovered by the Supernova Cosmology Project collaboration on 5 March 1997. The search technique finds such sets of high-redshift supernovae on the rising part of their light curves and guarantees the date of discovery, thus allowing follow-up photometry and spectroscopy of the transient supernovae to be scheduled. The supernova light curves were followed with scheduled R-, I- and some B-band photometry at the INT and other telescopes, among them, the Hubble Space Telescope. SN1997ap at z=0.83 is plotted on this Hubble diagram (effective B-magnitude at maximum versus redshift) also with the 5 high-redshift supernovae that could be width-luminosity corrected, and 18 from the lower-redshift Calan/Tololo Supernova Survey. Magnitudes have been K-corrected, and also corrected for the width-luminosity relation. The inner error bar on the SN1997ap point corresponds to the photometry error alone, while the outer error bar includes the intrinsic dispersion of type Ia supernovae after strech correction. The solid curves are theoretical m_B for (Omega_Matter, Omega_Lambda)=(0,0) on top, (1,0) in middle and (2,0) on bottom. The dotted curves are for the flat-universe case, with (Omega_Matter,Omega_Lambda)=(0,1) on top, (0.5,0.5), (1,0) and (1.5, -0.5) on bottom.[tiff,3.4M] [poscript,71k]