  We study a general phase transition between spinless topological nodal-line
semimetal and Weyl semimetal phases. We classify topological nodal lines into
two types based on their positions and shapes, and their phase transitions
depends on their types. We show that the topological nodal-line semimetal
becomes the Weyl semimetal by breaking time-reversal symmetry when the nodal
lines enclose time-reversal invariant momenta (type-A nodal lines). We also
discuss an effect of crystallographic symmetries determining the band structure
of the topological nodal-line semimetals. Thanks to protection by the
symmetries, the topological nodal-line semimetals can transit into the spinless
Weyl semimetals or maintain the nodal lines in many crystals after inversion
symmetry is broken.
