To provide an offset printing apparatus capable of suppressing the deterioration of printing precision by properly detecting a degree of the swelling of a blanket for printing swelled by an ink solvent by a simple configuration, and an offset printing method using the apparatus.

The offset printing apparatus 1 is provided with a blanket 2 for printing including an elastomer layer constituted of insulative rubber dispersed with conductive powder, a solvent aspirating means (a solvent removing means) 11 for removing an ink solvent permeated into an elastomer layer, and a volume resistivity measuring means (a conductivity measuring means) 21 for measuring the conductivity of the elastomer layer. Using the offset printing apparatus, the offset printing method comprises steps for transferring an ink carried on an ink receiving face to a printing medium 20 (a printing process), measuring the conductivity of the elastomer layer after a printing process by the volume resistivity measuring means 21 (a conductivity measuring process), and further removing the ink solvent from the elastomer layer on the basis of the conductivity of the elastomer layer measured by the conductivity measuring process (a solvent removing process).

COPYRIGHT: (C)2009,JPO&INPIT