  A rapidly rotating neutron star with strong magnetic fields, called magnetar,
is a possible candidate for the central engine of long gamma-ray bursts and
hypernovae (HNe). We solve the evolution of a shock wave driven by the wind
from magnetar and evaluate the temperature evolution, by which we estimate the
amount of $^{56}$Ni that produces a bright emission of HNe. We obtain a
constraint on the magnetar parameters, namely the poloidal magnetic field
strength ($B_p$) and initial angular velocity ($\Omega_i$), for synthesizing
enough $^{56}$Ni mass to explain HNe ($M_{^{56}\mathrm{Ni}}\gtrsim
0.2M_\odot$), i.e.
$(B_p/10^{16}~\mathrm{G})^{1/2}(\Omega_i/10^4~\mathrm{rad~s}^{-1})\gtrsim 0.7$.
