An electronic component mounting method of thermo-compressing and mounting electronic components onto a plurality of unit boards segmented in a multi-piece board which avoids the occurrence of adverse thermal influences on the thermosetting bonding material which is placed on the unit boards before mounting the electronic components. The thermo-compression tool used in the method is removably fitted on a thermo-compression head in an electronic component mounting apparatus; the thermo-compression tool includes a base member and a suck-up member which is smaller than a lower surface of the base member and which is fixed on the lower surface of the base member at a position displaced from a center thereof.