A synchronized driving assist apparatus includes: a first acceleration power spectrum acquisition section that acquires a first acceleration power spectrum according to acceleration of a first vehicle; a second acceleration power spectrum acquisition section that acquires a second acceleration power spectrum according to acceleration of a second vehicle; a cross power spectrum calculation section that calculates a cross power spectrum between the first vehicle and the second vehicle by using the first acceleration power spectrum and the second acceleration power spectrum; a coherence calculation section that calculates coherence from the cross power spectrum; and a correlation evaluation section that evaluates correlation in a synchronized driving of the first vehicle and the second vehicle on the basis of the coherence.