An in-vehicle communication support system mounted on an automobile having a first seat and a second seat that are seats arranged right and left in a front direction of the automobile and a third seat that is a seat arranged, in a front-rear direction, rear of the first seat and the second seat, wherein the in-vehicle communication support system comprises: a first microphone that is a microphone disposed in proximity to the first seat; a second microphone that is a microphone disposed in proximity to the second seat; a speaker configured to output sound toward the third seat; characterized by a signal processing unit configured to generate a speech voice of a user in the first seat and a speech voice of a user in the second seat to be output to the speaker by using an output of the first microphone and an output of the second microphone, wherein the signal processing unit includes, assuming that a voice having a sound source position at a speech position of the user in the first seat is a first seat voice, a first filter configured to convert the first seat voice collected by the second microphone into the first seat voice collected by a first seat virtual microphone that is a virtual microphone located at a position closer to the first seat than the second microphone, and outputs the first seat voice, a second filter configured to extract and output a component of the first seat voice from an output of the first filter, a delay unit configured to delay and output the output of the first microphone, a third filter configured to extract and output a component of the first seat voice from an output of the delay unit, and an addition unit configured to add an output of the second filter and an output of the third filter to generate the speech voice of the user in the first seat to be output to the speaker, and the delay unit configured to delay the output of the first microphone such that delay times of the component of the first seat voice output from the second filter and the component of the first seat voice output from the third filter match. a first microphone that is a microphone disposed in proximity to the first seat; a second microphone that is a microphone disposed in proximity to the second seat; a speaker configured to output sound toward the third seat; characterized by a signal processing unit configured to generate a speech voice of a user in the first seat and a speech voice of a user in the second seat to be output to the speaker by using an output of the first microphone and an output of the second microphone, wherein the signal processing unit includes, assuming that a voice having a sound source position at a speech position of the user in the first seat is a first seat voice, a first filter configured to convert the first seat voice collected by the second microphone into the first seat voice collected by a first seat virtual microphone that is a virtual microphone located at a position closer to the first seat than the second microphone, and outputs the first seat voice, a second filter configured to extract and output a component of the first seat voice from an output of the first filter, a delay unit configured to delay and output the output of the first microphone, a third filter configured to extract and output a component of the first seat voice from an output of the delay unit, and an addition unit configured to add an output of the second filter and an output of the third filter to generate the speech voice of the user in the first seat to be output to the speaker, and the delay unit configured to delay the output of the first microphone such that delay times of the component of the first seat voice output from the second filter and the component of the first seat voice output from the third filter match.