An ECU 10 for controlling execution of forced regeneration that removes PM deposited on a DPF by increasing a temperature of the DPF in an exhaust gas treatment device of a diesel engine including a DOC disposed in an exhaust passage and the DPF disposed downstream of the DOC includes: a determination unit 102 for determining whether an injection start condition corresponding to a remaining SOF deposition amount on the DOC is satisfied after the forced regeneration starts and after an upstream temperature of the DOC reaches a predetermined temperature; and an injection execution unit 104 for starting late-post injection of fuel to the DOC when the injection start condition is satisfied.