Photoinduced trion absorption in the time- and spectrum-resolved circular dichroism (CD) of a pristine WSe2 monolayer is manifested by a pronounced trion transition when the circular polarization of a probe pulse is opposite to that of the preceding pump pulse. Valley-polarized trion absorption enables visualization of the intervalley scattering dynamics of spin-polarized carriers, revealing a large excitation dependence that supports the valley depolarization through carrier-carrier scattering. Moreover, the CD and the Faraday rotation, which are both dominated by the spin-polarized shift of the A-exciton absorbance and the photoinduced trion transition, are confirmed to satisfy the Kramers-Kronig relationship between each other.