A method to determine welding conditions, comprising: a first step of receiving object-to-be-welded information, which is information about an object to be welded; a second step of receiving welding method information, which is information about an arc welding method; a third step of calculating a necessary quantity of arc heat, which is based on the object-to-be-welded information and the welding method information; and characterized by: a fourth step of calculating a wire feed speed as a recommended wire feed speed, a leg length as a recommended leg length, a welding speed as a recommended welding speed, a welding current as a recommended welding current, and a welding voltage as a recommended welding voltage, which are based on the object-to-be-welded information, the welding method information, and the necessary quantity of arc heat; a fifth step of changing the leg length from the recommended leg length to a determined leg length; and a sixth step of determining the wire feed speed as a determined wire feed speed, the welding current as a determined welding current and the welding voltage as a determined welding voltage, which are based on the determined leg length, the wire feed speed being calculated based on a formula for calculating the wire feed speed, which is in proportion to a square of the leg length and also in proportion to the welding speed, the welding current being calculated from the wire feed speed based either on a formula for calculating the welding current, which increases with an increase in the wire feed speed, or on a table showing the relation between the wire feed speed and the welding current, and the welding voltage being calculated from the calculated welding current, wherein the recommended welding speed is not changed and is determined as a determined welding speed. a first step of receiving object-to-be-welded information, which is information about an object to be welded; a second step of receiving welding method information, which is information about an arc welding method; a third step of calculating a necessary quantity of arc heat, which is based on the object-to-be-welded information and the welding method information; a fourth step of calculating a wire feed speed as a recommended wire feed speed, a leg length as a recommended leg length, a welding speed as a recommended welding speed, a welding current as a recommended welding current, and a welding voltage as a recommended welding voltage, which are based on the object-to-be-welded information, the welding method information, and the necessary quantity of arc heat; a fifth step of changing the leg length from the recommended leg length to a determined leg length; and a sixth step of determining the wire feed speed as a determined wire feed speed, the welding current as a determined welding current and the welding voltage as a determined welding voltage, which are based on the determined leg length, the wire feed speed being calculated based on a formula for calculating the wire feed speed, which is in proportion to a square of the leg length and also in proportion to the welding speed, the welding current being calculated from the wire feed speed based either on a formula for calculating the welding current, which increases with an increase in the wire feed speed, or on a table showing the relation between the wire feed speed and the welding current, and the welding voltage being calculated from the calculated welding current,