  We propose an unconventional type of Hall effect in a topological Dirac
semimetal with ferromagnetic electrodes. The topological Dirac semimetal itself
has time-reversal symmetry, whereas attached ferromagnetic electrodes break it,
causing the large Hall response. This induced Hall effect is a characteristic
of the helical surface/edge states that arise in topological materials, such as
topological Dirac semimetals or quantum spin Hall insulators. We compute the
Hall conductance/resistance and the Hall angle by using a lattice model with
four-terminal geometry. For topological Dirac semimetals with four electrodes,
the induced Hall effect occurs whether the current electrodes or the voltage
electrodes are ferromagnetic. When the spins in electrodes are almost fully
polarized, the Hall angle becomes as large as that of quantum Hall states or
ideal magnetic Weyl semimetals. We show the robustness of the induced Hall
effect against impurities and also discuss the spin injection and spin decay
problems. This Hall response can be used to detect whether the magnetizations
of the two ferromagnetic electrodes are parallel or antiparallel.
