Safety switch input diagnosis device and work machine using safety switch input diagnosis device

A safety switch input diagnosis device, comprising:

• a first circuit formed from a series connection of a switch capable of interrupting connection between a first contact and a second contact and a line having a first resistor connected to the first or the second contact of the switch;
• a second circuit having a second resistor between one end and another end and connected at the one end to one end of the first circuit;
• a third circuit connected at one end to the other end of the second circuit and at another end to a power supply;
• a fourth circuit connected at one end to another end of the first circuit;
• a fifth circuit having a third resistor between one end and another end and connected at the one end to another end of the fourth circuit and at the other end to a ground;
• a sixth circuit having a fourth resistor between one end and another end and connected at the one end to the one end of the first circuit and at the other end to the other end of the first circuit;
• a seventh circuit connected at one end to the other end of the first circuit;
• an eighth circuit having a fifth resistor between one end and another end and connected at the one end to another end of the seventh circuit and at the other end to the ground;
• and
• a controller that diagnoses a connection state of the switch and failure modes of the third, the fourth, and the seventh circuits on a basis of a voltage value at the one end of the eighth circuit and outputs a result of diagnosis.