A method for manufacturing a power module substrate with heat sink, comprising the steps of: forming a circuit layer on one surface of an insulating layer; forming a metal layer on the other surface of the insulating layer; and bonding a heat sink on a surface of the metal layer on a side opposite to the insulating layer by solid-phase diffusion bonding, characterized in that a bonding surface of the metal layer to be bonded with the heat sink and a bonding surface of the heat sink to be bonded with the metal layer are constituted by an aluminum material including aluminum or an aluminum alloy, the aluminum material that constitutes the bonding surface of the metal layer to be bonded with the heat sink is set to a high-purity aluminum material with high aluminum purity, and the aluminum material that constitutes the bonding surface of the heat sink to be bonded with the metal layer is set to a low-purity aluminum material with low aluminum purity, the high-purity aluminum material and the low-purity aluminum material contain one kind or two or more kinds of elements selected from Si, Cu, Mn, Fe, Mg, Zn, Ti, and Cr as the contained elements other than Al, and a difference between a total amount of the contained elements other than Al in the high-purity aluminum material and a total amount of the contained elements other than Al in the low-purity aluminum material is set to 1 at% or greater the bonding step includes laminating the metal layer and the heat sink while applying a load of 0.3 MPa to 3.0 MPa to the resultant laminated body in a lamination direction, and retaining the laminated body at a temperature that is equal to or higher than 90% of a solidus temperature of the low-purity aluminum material and is lower than the solidus temperature of the low-purity aluminum material for 1 hour or longer to subject the metal layer and the heat sink to the solid-phase diffusion bonding. forming a circuit layer on one surface of an insulating layer; forming a metal layer on the other surface of the insulating layer; and bonding a heat sink on a surface of the metal layer on a side opposite to the insulating layer by solid-phase diffusion bonding, characterized in that a bonding surface of the metal layer to be bonded with the heat sink and a bonding surface of the heat sink to be bonded with the metal layer are constituted by an aluminum material including aluminum or an aluminum alloy, the aluminum material that constitutes the bonding surface of the metal layer to be bonded with the heat sink is set to a high-purity aluminum material with high aluminum purity, and the aluminum material that constitutes the bonding surface of the heat sink to be bonded with the metal layer is set to a low-purity aluminum material with low aluminum purity, the high-purity aluminum material and the low-purity aluminum material contain one kind or two or more kinds of elements selected from Si, Cu, Mn, Fe, Mg, Zn, Ti, and Cr as the contained elements other than Al, and a difference between a total amount of the contained elements other than Al in the high-purity aluminum material and a total amount of the contained elements other than Al in the low-purity aluminum material is set to 1 at% or greater the bonding step includes laminating the metal layer and the heat sink while applying a load of 0.3 MPa to 3.0 MPa to the resultant laminated body in a lamination direction, and retaining the laminated body at a temperature that is equal to or higher than 90% of a solidus temperature of the low-purity aluminum material and is lower than the solidus temperature of the low-purity aluminum material for 1 hour or longer to subject the metal layer and the heat sink to the solid-phase diffusion bonding.