In a transmission circuit board, ground terminal portions (10) are disposed at every other two rows in both end columns. Each of signal circuit layers (20) includes at least a pair of adjacent signal connecting portions electrically connected to a pair of the wiring portions (21, 22) arranged in parallel in a row direction and the column direction different from those on an adjacent signal circuit layer. Each of the ground layers is electrically connected to at least one of the ground terminal portions (10) in the both end columns.