A welding method includes sandwiching a first base material and a second base material between a first block and a second block, the first and second base materials being made of a light-transmitting resin, and welding the first and second base materials to each other by making a laser beam enter the second base material through a front surface of the second base material toward the first block from outside an outline of the second block at an acute entry angle with respect to the front surface of the second base material and by focusing the laser beam on the first and second base materials between the first and second blocks.