  Magnetic-field-angle-resolved specific heat and magnetization measurements
were conducted on a ferromagnetic superconductor UCoGe with remarkable
anisotropic upper critical field $H_{\rm c2}$. Although $H_{\rm c2}$ reaches a
high magnetic field ($\sim 20$~T) along the $b$ axis, it is small
($\sim~0.6$~T) when a magnetic field is applied along the magnetic easy
$c$-axis. This study indicates that the specific heat is abruptly suppressed
when the magnetic field is applied toward the $c$ axis from the $a$ and $b$
axes in the ferromagnetic state. The field response of density of states (DOS)
is anisotropic, relative to the $c$ axis, and its angle dependence is slightly
singular. The Ising-type magnetic anisotropy of the ferromagnetic state is
dominant even in the anisotropic reinforced superconducting state. These facts
indicate that the suppression of DOS may closely relate to the superconducting
state. We theoretically analyze these findings together with URhGe and UTe$_2$
by highlighting the common and distinctive features among three compounds.
