An electronic circuit device comprising: an insulating layer , a conductor layer provided on at least one face side of the insulating layer, and a heat generating element provided on a face of the conductor layer at a side opposite of the insulating layer via a joining layer , wherein the conductor layer has a heat dissipating conductor layer located on a heat generating element side and a circuit layer located on the insulating layer side, and a shortest distance l 1 between a side end portion of the heat generating element and a side end portion of the heat dissipating conductor layer on a face of the heat dissipating conductor layer on the circuit layer side is greater than or equal to a thickness t 1 of the heat dissipating conductor layer, wherein the conductor layer has an intervening metal layer between the heat dissipating conductor layer and the circuit layer, characterized in that the intervening metal layer is a sintered body of metal particles, that the intervening metal layer has a layer inner portion that is in contact with a face of the heat dissipating conductor layer and a layer outer portion that extends to surround a side edge of the heat dissipating conductor layer, and the layer outer portion has a porosity higher than a porosity of the layer inner portion, and that for the intervening metal layer the ratio [(B)/(A)] of the porosity (B) at an intermediate part in the thickness direction of the layer outer portion to the porosity (A) at an intermediate part in the thickness direction of the inner portion is 1.10 to 1.60 and the porosity (A) of the layer inner portion is 10.5% to 20.0%.. an insulating layer , a conductor layer provided on at least one face side of the insulating layer, and a heat generating element provided on a face of the conductor layer at a side opposite of the insulating layer via a joining layer , wherein the conductor layer has a heat dissipating conductor layer located on a heat generating element side and a circuit layer located on the insulating layer side, and a shortest distance l 1 between a side end portion of the heat generating element and a side end portion of the heat dissipating conductor layer on a face of the heat dissipating conductor layer on the circuit layer side is greater than or equal to a thickness t 1 of the heat dissipating conductor layer, wherein the conductor layer has an intervening metal layer between the heat dissipating conductor layer and the circuit layer, characterized in that the intervening metal layer is a sintered body of metal particles, that the intervening metal layer has a layer inner portion that is in contact with a face of the heat dissipating conductor layer and a layer outer portion that extends to surround a side edge of the heat dissipating conductor layer, and the layer outer portion has a porosity higher than a porosity of the layer inner portion, and that for the intervening metal layer the ratio [(B)/(A)] of the porosity (B) at an intermediate part in the thickness direction of the layer outer portion to the porosity (A) at an intermediate part in the thickness direction of the inner portion is 1.10 to 1.60 and the porosity (A) of the layer inner portion is 10.5% to 20.0%.. <EOS>