A ceramic circuit substrate formed by bonding a ceramic substrate and a copper plate via a brazing material comprising Ag, Cu, and an active metal, wherein a bond void fraction is no greater than 1.0%, a distance between the surface of the ceramic substrate and the portion at which the Ag diffused furthest from the surface of the ceramic substrate is 5-20 μm, a crack rate after heat cycles is no greater than 1.0%, the distance is measured by observing, at a magnification of 500× in a scanning electron microscope, 3 fields of view randomly selected from a cross-section of the ceramic circuit substrate with a 250 μm range in the horizontal direction of the bonding interface, such that the ranges do not overlap, and is the largest diffusion distance of the Ag OrCm among those measured in the fields of view, the bond void fraction is determined by measuring the surface area of the bond voids of the ceramic circuit substrate observed with an ultrasonic flaw detector and dividing by the surface area of the copper circuit pattern, and the crack rate is measured by performing with one heat cycle defined as being kept for 5 minutes on a hot plate at 350°C, 5 minutes at 25°C, 5 minutes at -78°C in dry ice, and 5 minutes at 25°C, 10 continuous cycles on the ceramic circuit substrate, and removing the copper plate, brazing material layer, and nitride layer by etching, capturing the horizontal cracks generated on the surface of the ceramic substrate at a resolution of 600 dpi × 600 dpi with a scanner, and calculating the crack rate by binarizing, with a threshold of 140, with the image analysis software GIMP2 and then dividing the horizontal crack surface area by the circuit pattern surface area. a bond void fraction is no greater than 1.0%, a distance between the surface of the ceramic substrate and the portion at which the Ag diffused furthest from the surface of the ceramic substrate is 5-20 μm, a crack rate after heat cycles is no greater than 1.0%, the distance is measured by observing, at a magnification of 500× in a scanning electron microscope, 3 fields of view randomly selected from a cross-section of the ceramic circuit substrate with a 250 μm range in the horizontal direction of the bonding interface, such that the ranges do not overlap, and is the largest diffusion distance of the Ag OrCm among those measured in the fields of view, the bond void fraction is determined by measuring the surface area of the bond voids of the ceramic circuit substrate observed with an ultrasonic flaw detector and dividing by the surface area of the copper circuit pattern, and the crack rate is measured by performing with one heat cycle defined as being kept for 5 minutes on a hot plate at 350°C, 5 minutes at 25°C, 5 minutes at -78°C in dry ice, and 5 minutes at 25°C, 10 continuous cycles on the ceramic circuit substrate, and removing the copper plate, brazing material layer, and nitride layer by etching, capturing the horizontal cracks generated on the surface of the ceramic substrate at a resolution of 600 dpi × 600 dpi with a scanner, and calculating the crack rate by binarizing, with a threshold of 140, with the image analysis software GIMP2 and then dividing the horizontal crack surface area by the circuit pattern surface area. <EOS>