Abstract The 1–70 keV persistent spectra of 15 magnetars, observed with Suzaku from 2006 to 2013, were studied as a complete sample. Combined with early NuSTAR observations of four hard X-ray emitters, nine objects showed a hard power-law emission dominating at keV with the 15–60 keV flux of ∼1– erg s−1 cm−2. The hard X-ray luminosity , relative to that of a soft-thermal surface radiation , tends to become higher toward younger and strongly magnetized objects. Their hardness ratio, updated from a previous study and defined as , is correlated with the measured spin-down rate as , corresponding to positive and negative correlations with the dipole field strength ( ) and the characteristic age ( ), respectively. Among our sample, five transients were observed during X-ray outbursts, and the results are compared with their long-term 1–10 keV flux decays monitored with Swift/XRT and RXTE/PCA. Fading curves of three bright outbursts are approximated by an empirical formula used in the seismology, showing a ∼10–40 day plateau phase. Transients show the maximum luminosities of ∼ 1035 erg s−1, which are comparable to those of persistently bright ones, and fade back to ≲1032 erg s−1. Spectral properties are discussed in the framework of the magnetar hypothesis.