A power transmission device includes power transmission coils arranged in a line, a power transmission circuit connected to the power transmission coils and supplying the AC power to the power transmission coils, and control circuitry that switches an electrical connection state between the power transmission circuit and each of the power transmission coils, detect a relative position between the power receiving coil and each of the power transmission coils, selects a number of power transmission coils adjacent to each other based on the detected relative position, the selected number of power transmission coils being fixed, and causes the power transmission circuit to supply the AC power to the selected number of power transmission coils. In an array direction of the power transmission coils, a width Dwt of each of the power transmission coils is shorter than a width Dwr of the power receiving coil and Dwt/Dwr≤0.875.